{"id":888,"date":"2025-05-19T22:52:24","date_gmt":"2025-05-19T22:52:24","guid":{"rendered":"https:\/\/science.gsfc.nasa.gov\/stella\/?page_id=888"},"modified":"2025-07-02T00:50:23","modified_gmt":"2025-07-02T00:50:23","slug":"spectral","status":"publish","type":"page","link":"https:\/\/science.gsfc.nasa.gov\/stella\/instruments\/spectral\/","title":{"rendered":"Spectral"},"content":{"rendered":"\t\t<div data-elementor-type=\"wp-page\" data-elementor-id=\"888\" class=\"elementor elementor-888\">\n\t\t\t\t<div class=\"elementor-element elementor-element-f2f437b e-flex e-con-boxed e-con e-parent\" data-id=\"f2f437b\" data-element_type=\"container\" data-settings=\"{&quot;background_background&quot;:&quot;classic&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-5142835 elementor-widget elementor-widget-heading\" data-id=\"5142835\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Spectral Instruments<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-5181568 e-flex e-con-boxed e-con e-parent\" data-id=\"5181568\" data-element_type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-56c95f6 elementor-widget elementor-widget-heading\" data-id=\"56c95f6\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">About STELLA Spectrometers<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-76d0172 e-flex e-con-boxed e-con e-parent\" data-id=\"76d0172\" data-element_type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t<div class=\"elementor-element elementor-element-90e98f6 e-con-full e-flex e-con e-child\" data-id=\"90e98f6\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-92de2b2 elementor-widget elementor-widget-text-editor\" data-id=\"92de2b2\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<h4><strong>A Note About STELLA Data<\/strong><\/h4><p>The performance of STELLA has not been scientifically peer-reviewed.<\/p><p>STELLA spectrometers provide users the ability to capture point-based spectral observations in the visible (VIS) and near infrared (NIR) bands of the Electromagnetic Spectrum. These spectrometers can be used over a variety of land cover surface targets such as urban areas, bare soils, grasses, and other vegetated surfaces.<\/p><p>The <a href=\"https:\/\/science.gsfc.nasa.gov\/stella\/\/instruments\/heliophysics\/\">Helio-STELLA<\/a>, while still a spectrometer, differs from the spectrometers\u00a0 mentioned here in that it is meant to look at the sun.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-930bb91 elementor-widget elementor-widget-text-editor\" data-id=\"930bb91\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p><a href=\"#calibrate\"><strong>Learn more about how we calculate reflectance and calibrate STELLA spectrometers.<\/strong><\/a><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-f2ee1c2 e-con-full e-flex e-con e-child\" data-id=\"f2ee1c2\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-5f9625a elementor-widget elementor-widget-image\" data-id=\"5f9625a\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t<figure class=\"wp-caption\">\n\t\t\t\t\t\t\t\t\t\t\t<a href=\"https:\/\/science.gsfc.nasa.gov\/stella\/\/wp-content\/uploads\/2025\/05\/2023STELLAinterns_field.jpg\" data-elementor-open-lightbox=\"yes\" data-elementor-lightbox-title=\"2023STELLAinterns_field\" data-e-action-hash=\"#elementor-action%3Aaction%3Dlightbox%26settings%3DeyJpZCI6ODA0LCJ1cmwiOiJodHRwczpcL1wvc2NpZW5jZS5nc2ZjLm5hc2EuZ292XC9zdGVsbGFcL3dwLWNvbnRlbnRcL3VwbG9hZHNcLzIwMjVcLzA1XC8yMDIzU1RFTExBaW50ZXJuc19maWVsZC5qcGcifQ%3D%3D\">\n\t\t\t\t\t\t\t<img fetchpriority=\"high\" decoding=\"async\" width=\"640\" height=\"480\" src=\"https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/2023STELLAinterns_field.jpg\" class=\"attachment-full size-full wp-image-804\" alt=\"Two high school NASA summer interns, Christina Ballagh and Sabrina Pillai, pose for a photo in front of GSFC Optical Engineer, Jesse Barber, during a field campaign to collect coincident data using STELLA and an ASD spectrometer at the USDA Beltsville Agricultural Research Center.\" srcset=\"https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/2023STELLAinterns_field.jpg 640w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/2023STELLAinterns_field-300x225.jpg 300w\" sizes=\"(max-width: 640px) 100vw, 640px\" \/>\t\t\t\t\t\t\t\t<\/a>\n\t\t\t\t\t\t\t\t\t\t\t<figcaption class=\"widget-image-caption wp-caption-text\">Two high school NASA summer interns, Christina Ballagh and Sabrina Pillai, pose for a photo in front of GSFC Optical Engineer, Jesse Barber, during a field campaign to collect coincident data using STELLA and an ASD spectrometer at the USDA Beltsville Agricultural Research Center.<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-9a9a536 e-flex e-con-boxed e-con e-parent\" data-id=\"9a9a536\" data-element_type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-a2b02aa elementor-widget elementor-widget-heading\" data-id=\"a2b02aa\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">STELLA-Q2<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-9526b7f e-con-full e-flex e-con e-child\" data-id=\"9526b7f\" data-element_type=\"container\">\n\t\t<div class=\"elementor-element elementor-element-7cf089f e-con-full e-flex e-con e-child\" data-id=\"7cf089f\" data-element_type=\"container\" data-settings=\"{&quot;background_background&quot;:&quot;classic&quot;}\">\n\t\t\t\t<div class=\"elementor-element elementor-element-a7f34dc elementor-widget elementor-widget-image\" data-id=\"a7f34dc\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<a href=\"\/stella\/instruments\/spectral\/stella-q2\/\">\n\t\t\t\t\t\t\t<img decoding=\"async\" width=\"899\" height=\"899\" src=\"https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/STELLA-Q2.png\" class=\"attachment-full size-full wp-image-663\" alt=\"STELLA-Q2 spectrometer photo\" srcset=\"https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/STELLA-Q2.png 899w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/STELLA-Q2-300x300.png 300w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/STELLA-Q2-150x150.png 150w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/STELLA-Q2-768x768.png 768w\" sizes=\"(max-width: 899px) 100vw, 899px\" \/>\t\t\t\t\t\t\t\t<\/a>\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-3a17ed3 e-con-full e-flex e-con e-child\" data-id=\"3a17ed3\" data-element_type=\"container\">\n\t\t<div class=\"elementor-element elementor-element-1b5d54b e-con-full e-flex e-con e-child\" data-id=\"1b5d54b\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-6e4c2b2 elementor-widget elementor-widget-text-editor\" data-id=\"6e4c2b2\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>The STELLA-Q2 takes measurements in 18 bands across a wavelength range of 410 \u2013 940 nm.<\/p><p><strong>Building this device does not require 3D printing or\u00a0soldering.<\/strong><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-f6887ba e-con-full e-flex e-con e-child\" data-id=\"f6887ba\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-cbdaaca elementor-widget__width-inherit elementor-widget elementor-widget-premium-addon-image-button\" data-id=\"cbdaaca\" data-element_type=\"widget\" data-widget_type=\"premium-addon-image-button.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\n\t\t<a class=\"premium-image-button-none premium-image-button premium-btn-sm premium-image-button-none\" href=\"\/stella\/instruments\/spectral\/stella-q2\/\">\n\t\t\t<div class=\"premium-image-button-text-icon-wrapper\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<svg class=\"premium-svg-nodraw premium-drawable-icon e-font-icon-svg e-fas-tools\" aria-hidden=\"true\" viewBox=\"0 0 512 512\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><path d=\"M501.1 395.7L384 278.6c-23.1-23.1-57.6-27.6-85.4-13.9L192 158.1V96L64 0 0 64l96 128h62.1l106.6 106.6c-13.6 27.8-9.2 62.3 13.9 85.4l117.1 117.1c14.6 14.6 38.2 14.6 52.7 0l52.7-52.7c14.5-14.6 14.5-38.2 0-52.7zM331.7 225c28.3 0 54.9 11 74.9 31l19.4 19.4c15.8-6.9 30.8-16.5 43.8-29.5 37.1-37.1 49.7-89.3 37.9-136.7-2.2-9-13.5-12.1-20.1-5.5l-74.4 74.4-67.9-11.3L334 98.9l74.4-74.4c6.6-6.6 3.4-17.9-5.7-20.2-47.4-11.7-99.6.9-136.6 37.9-28.5 28.5-41.9 66.1-41.2 103.6l82.1 82.1c8.1-1.9 16.5-2.9 24.7-2.9zm-103.9 82l-56.7-56.7L18.7 402.8c-25 25-25 65.5 0 90.5s65.5 25 90.5 0l123.6-123.6c-7.6-19.9-9.9-41.6-5-62.7zM64 472c-13.2 0-24-10.8-24-24 0-13.3 10.7-24 24-24s24 10.7 24 24c0 13.2-10.7 24-24 24z\"><\/path><\/svg>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\t\t<span >\n\t\t\t\t\t\tBuild a STELLA-Q2\t\t\t\t\t<\/span>\n\t\t\t\t\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\n\t\t\t\n\t\t\t\n\t\t\t\n\t\t<\/a>\n\n\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-295d234 e-flex e-con-boxed e-con e-parent\" data-id=\"295d234\" data-element_type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-643c695 elementor-widget elementor-widget-heading\" data-id=\"643c695\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">STELLA-1.1<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-85a92e8 e-con-full e-flex e-con e-child\" data-id=\"85a92e8\" data-element_type=\"container\">\n\t\t<div class=\"elementor-element elementor-element-26a712b e-con-full e-flex e-con e-child\" data-id=\"26a712b\" data-element_type=\"container\" data-settings=\"{&quot;background_background&quot;:&quot;classic&quot;}\">\n\t\t\t\t<div class=\"elementor-element elementor-element-429f4d9 elementor-widget elementor-widget-image\" data-id=\"429f4d9\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<a href=\"\/stella\/instruments\/spectral\/stella-1-1\/\">\n\t\t\t\t\t\t\t<img decoding=\"async\" width=\"899\" height=\"899\" src=\"https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2023\/11\/STELLA-1_1.png\" class=\"attachment-full size-full wp-image-1259\" alt=\"STELLA-1.1 spectrometer\" srcset=\"https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2023\/11\/STELLA-1_1.png 899w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2023\/11\/STELLA-1_1-300x300.png 300w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2023\/11\/STELLA-1_1-150x150.png 150w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2023\/11\/STELLA-1_1-768x768.png 768w\" sizes=\"(max-width: 899px) 100vw, 899px\" \/>\t\t\t\t\t\t\t\t<\/a>\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-f07a8ae e-con-full e-flex e-con e-child\" data-id=\"f07a8ae\" data-element_type=\"container\">\n\t\t<div class=\"elementor-element elementor-element-dc43d91 e-con-full e-flex e-con e-child\" data-id=\"dc43d91\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-e78f48b elementor-widget elementor-widget-text-editor\" data-id=\"e78f48b\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>The STELLA-1.1 takes measurements in 12 bands across a wavelength range of 450 \u2013 860 nm and includes surface temperature and weather sensors.\u00a0<\/p><p><strong>Requires 3D printing and soldering to build<\/strong><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-ac9c8b0 e-con-full e-flex e-con e-child\" data-id=\"ac9c8b0\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-15f9392 elementor-widget__width-inherit elementor-widget elementor-widget-premium-addon-image-button\" data-id=\"15f9392\" data-element_type=\"widget\" data-widget_type=\"premium-addon-image-button.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\n\t\t<a class=\"premium-image-button-none premium-image-button premium-btn-sm premium-image-button-none\" href=\"\/stella\/instruments\/spectral\/stella-1-1\/\">\n\t\t\t<div class=\"premium-image-button-text-icon-wrapper\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<svg class=\"premium-svg-nodraw premium-drawable-icon e-font-icon-svg e-fas-tools\" aria-hidden=\"true\" viewBox=\"0 0 512 512\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><path d=\"M501.1 395.7L384 278.6c-23.1-23.1-57.6-27.6-85.4-13.9L192 158.1V96L64 0 0 64l96 128h62.1l106.6 106.6c-13.6 27.8-9.2 62.3 13.9 85.4l117.1 117.1c14.6 14.6 38.2 14.6 52.7 0l52.7-52.7c14.5-14.6 14.5-38.2 0-52.7zM331.7 225c28.3 0 54.9 11 74.9 31l19.4 19.4c15.8-6.9 30.8-16.5 43.8-29.5 37.1-37.1 49.7-89.3 37.9-136.7-2.2-9-13.5-12.1-20.1-5.5l-74.4 74.4-67.9-11.3L334 98.9l74.4-74.4c6.6-6.6 3.4-17.9-5.7-20.2-47.4-11.7-99.6.9-136.6 37.9-28.5 28.5-41.9 66.1-41.2 103.6l82.1 82.1c8.1-1.9 16.5-2.9 24.7-2.9zm-103.9 82l-56.7-56.7L18.7 402.8c-25 25-25 65.5 0 90.5s65.5 25 90.5 0l123.6-123.6c-7.6-19.9-9.9-41.6-5-62.7zM64 472c-13.2 0-24-10.8-24-24 0-13.3 10.7-24 24-24s24 10.7 24 24c0 13.2-10.7 24-24 24z\"><\/path><\/svg>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\t\t<span >\n\t\t\t\t\t\tBuild a STELLA-1.1\t\t\t\t\t<\/span>\n\t\t\t\t\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\n\t\t\t\n\t\t\t\n\t\t\t\n\t\t<\/a>\n\n\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-8722cf5 e-flex e-con-boxed e-con e-parent\" data-id=\"8722cf5\" data-element_type=\"container\" id=\"calibrate\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t<div class=\"elementor-element elementor-element-6ed3fae e-con-full e-flex e-con e-child\" data-id=\"6ed3fae\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-fc285f0 e-n-tabs-mobile elementor-widget elementor-widget-n-tabs\" data-id=\"fc285f0\" data-element_type=\"widget\" data-settings=\"{&quot;tabs_justify_horizontal&quot;:&quot;center&quot;,&quot;horizontal_scroll&quot;:&quot;disable&quot;}\" data-widget_type=\"nested-tabs.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<div class=\"e-n-tabs\" data-widget-number=\"264406512\" aria-label=\"Tabs. Open items with Enter or Space, close with Escape and navigate using the Arrow keys.\">\n\t\t\t<div class=\"e-n-tabs-heading\" role=\"tablist\">\n\t\t\t\t\t<button id=\"e-n-tab-title-2644065121\" class=\"e-n-tab-title\" aria-selected=\"true\" data-tab-index=\"1\" role=\"tab\" tabindex=\"0\" aria-controls=\"e-n-tab-content-2644065121\" style=\"--n-tabs-title-order: 1;\">\n\t\t\t\t\t\t<span class=\"e-n-tab-title-text\">\n\t\t\t\tCalculating Reflectance\t\t\t<\/span>\n\t\t<\/button>\n\t\t\t\t<button id=\"e-n-tab-title-2644065122\" class=\"e-n-tab-title\" aria-selected=\"false\" data-tab-index=\"2\" role=\"tab\" tabindex=\"-1\" aria-controls=\"e-n-tab-content-2644065122\" style=\"--n-tabs-title-order: 2;\">\n\t\t\t\t\t\t<span class=\"e-n-tab-title-text\">\n\t\t\t\tLimitations &amp; Considerations\t\t\t<\/span>\n\t\t<\/button>\n\t\t\t\t<button id=\"e-n-tab-title-2644065123\" class=\"e-n-tab-title\" aria-selected=\"false\" data-tab-index=\"3\" role=\"tab\" tabindex=\"-1\" aria-controls=\"e-n-tab-content-2644065123\" style=\"--n-tabs-title-order: 3;\">\n\t\t\t\t\t\t<span class=\"e-n-tab-title-text\">\n\t\t\t\tSpectrometer Measurements\t\t\t<\/span>\n\t\t<\/button>\n\t\t\t\t<button id=\"e-n-tab-title-2644065124\" class=\"e-n-tab-title\" aria-selected=\"false\" data-tab-index=\"4\" role=\"tab\" tabindex=\"-1\" aria-controls=\"e-n-tab-content-2644065124\" style=\"--n-tabs-title-order: 4;\">\n\t\t\t\t\t\t<span class=\"e-n-tab-title-text\">\n\t\t\t\tCalibration Q&amp;A\t\t\t<\/span>\n\t\t<\/button>\n\t\t\t\t\t<\/div>\n\t\t\t<div class=\"e-n-tabs-content\">\n\t\t\t\t<div id=\"e-n-tab-content-2644065121\" role=\"tabpanel\" aria-labelledby=\"e-n-tab-title-2644065121\" data-tab-index=\"1\" style=\"--n-tabs-title-order: 1;\" class=\"e-active elementor-element elementor-element-50b1cb8 e-con-full e-flex e-con e-child\" data-id=\"50b1cb8\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-09e6d74 elementor-widget elementor-widget-heading\" data-id=\"09e6d74\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Calculating Reflectance from STELLA Data<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-b3e6c1d elementor-widget elementor-widget-text-editor\" data-id=\"b3e6c1d\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>STELLA spectrometers measure incoming light as irradiance in microwatts per centimeter squared (uW\/cm\u00b2), and must be converted to reflectance when comparing measurements over different targets.<\/p><p>To calculate reflectance, collect coincident calibration measurements using a white reference panel.<\/p><p>Affordable <strong>reference panels<\/strong> we recommend:\u00a0<\/p><ul><li>Polystyrene foam (not smooth or shiny) &#8211; this is our #1 pick<\/li><li>Opaque white cutting board<\/li><li>Playground sand<\/li><li>White paper (a few sheets thick to make opaque)<\/li><\/ul><p>Ensure the target and reference measurements are collected using the same acquisition geometries, light levels, and distance between the device and the target or panel*. Record the distance from the device to, and the area of, the target.<\/p><p>Using the raw irradiance values collected by STELLA, the distance in cm, and the area, calculate radiance for both the target and the reference observations:<\/p><p><strong>Radiance (uW\/cm\u00b2) = Irradiance * Distance\u00b2\/Area<\/strong><\/p><p>From the calculated radiance of the target and the white reference, calculate reflectance of the observed target:<\/p><p><strong>Reflectance (%) = Radiance of target \/ Radiance of reference<\/strong><\/p><p>*An easy way to ensure measurements of the target and reference panel are taken under the same conditions is by following the \u2018sandwich\u2019 method, which consists of collecting a sequence of panel-target-panel measurements and using the average of the two reference panel readings for calculating reflectance.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div id=\"e-n-tab-content-2644065122\" role=\"tabpanel\" aria-labelledby=\"e-n-tab-title-2644065122\" data-tab-index=\"2\" style=\"--n-tabs-title-order: 2;\" class=\" elementor-element elementor-element-e8dc5eb e-con-full e-flex e-con e-child\" data-id=\"e8dc5eb\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-167df1f elementor-widget elementor-widget-heading\" data-id=\"167df1f\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Limitations and Considerations<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-7bcc871 elementor-widget elementor-widget-text-editor\" data-id=\"7bcc871\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>While it is possible to obtain reliable measurements over short, uniform vegetation canopies and flat surface targets, limitations exist when collecting data over surfaces with diverse Bidirectional Reflectance Distribution Function (BRDF) properties. Surfaces with heterogeneous texture and vertical canopy structure (e.g., tall corn or forest canopies) are associated with an increase in measurement uncertainty. To derive accurate spectral measurements, the BRDF properties of the target land cover must be considered. To enable comparison between observations, it is important to maintain consistent acquisition geometry and light levels between measurements.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-70a2022 e-flex e-con-boxed e-con e-child\" data-id=\"70a2022\" data-element_type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t<div class=\"elementor-element elementor-element-b96ec1b e-con-full e-flex e-con e-child\" data-id=\"b96ec1b\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-da55142 elementor-widget elementor-widget-text-editor\" data-id=\"da55142\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>STELLA data was evaluated against measurements collected with an Analytical Spectral Devices spectrometer (ASD). An ASD is a common field instrument, calibrated to radiance, that provides stable reflectance estimates in the 400 \u2013 2,500 nm region with a 3 nm spectral resolution. STELLA and ASD data were both collected in situ using a white panel target under consistent light and acquisition (sun-sensor-target) geometry conditions.<\/p><p>While the STELLA reflectance measurements were significantly higher than those collected using the ASD, the two datasets were strongly correlated under these conditions and no significant differences in uncertainty were observed (figure). Generally, the standard deviation of the data were found to vary between 8 \u2013 18% while the standard errors were found in the range of 3 \u2013 6%, with the VIS bands having lower uncertainties than those in the red-edge and NIR bands.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-1d344af e-con-full e-flex e-con e-child\" data-id=\"1d344af\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-9b3c72b elementor-widget elementor-widget-image\" data-id=\"9b3c72b\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t<figure class=\"wp-caption\">\n\t\t\t\t\t\t\t\t\t\t\t<a href=\"https:\/\/science.gsfc.nasa.gov\/stella\/\/wp-content\/uploads\/2025\/05\/STELLA_ASD_plot.png\" data-elementor-open-lightbox=\"yes\" data-elementor-lightbox-title=\"STELLA_ASD_plot\" data-e-action-hash=\"#elementor-action%3Aaction%3Dlightbox%26settings%3DeyJpZCI6ODA1LCJ1cmwiOiJodHRwczpcL1wvc2NpZW5jZS5nc2ZjLm5hc2EuZ292XC9zdGVsbGFcL3dwLWNvbnRlbnRcL3VwbG9hZHNcLzIwMjVcLzA1XC9TVEVMTEFfQVNEX3Bsb3QucG5nIn0%3D\">\n\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"512\" height=\"449\" src=\"https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/STELLA_ASD_plot.png\" class=\"attachment-full size-full wp-image-805\" alt=\"Comparison of white panel measurements collected with STELLA 1.1 and ASD using the same sun-sensor-target geometry. The points represent the average values and the length of the bars represent the standard deviations among measurements observed by the ASD (x-axis) and STELLA (y-axis) for the 12 spectral bands. These results are preliminary and have not yet been peer-reviewed.\" srcset=\"https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/STELLA_ASD_plot.png 512w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/STELLA_ASD_plot-300x263.png 300w\" sizes=\"(max-width: 512px) 100vw, 512px\" \/>\t\t\t\t\t\t\t\t<\/a>\n\t\t\t\t\t\t\t\t\t\t\t<figcaption class=\"widget-image-caption wp-caption-text\">Comparison of white panel measurements collected with STELLA 1.1 and ASD using the same sun-sensor-target geometry. The points represent the average values and the length of the bars represent the standard deviations among measurements observed by the ASD (x-axis) and STELLA (y-axis) for the 12 spectral bands. These results are preliminary and have not yet been peer-reviewed.<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div id=\"e-n-tab-content-2644065123\" role=\"tabpanel\" aria-labelledby=\"e-n-tab-title-2644065123\" data-tab-index=\"3\" style=\"--n-tabs-title-order: 3;\" class=\" elementor-element elementor-element-9d2e12a e-con-full e-flex e-con e-child\" data-id=\"9d2e12a\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-949b324 elementor-widget elementor-widget-heading\" data-id=\"949b324\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">What do the STELLA spectrometers measure?<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-b374609 elementor-widget elementor-widget-text-editor\" data-id=\"b374609\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p><strong>STELLA-Q2 \u2013 Light intensity (uW\/cm2), in the visible and near infrared wavelengths (in nanometers): 410, 435, 460, 485, 510, 535, 560, 585, 610, 645, 680, 705, 730, 760, 810, 860, 900, 940<\/strong><\/p><p>The light intensity is measured in microwatts per centimeters squared, with error bars of +\/- 12% of the value. The sensor selects the specific wavelength bands by using a set of silicon thin-film interference filters, to a precision of +\/- 5 nanometers. The bands are centered around the wavelengths listed above, and the bandwidth of each band is +\/- 10 nanometers full-width half-maximum around the band center, in a Gaussian distribution of sensitivity. Silicon is a hard material with low thermal expansivity, so the sensor characteristics are stable over a broad temperature range, as well as over the life of the sensor. The sensor\u2019s field of view is cone-shaped, with a cone angle of +\/- 20\u00b0 for a total field of view of 40\u00b0.<\/p><p><strong>STELLA-Q, 1.0, 1.1 and 2.0 \u2013 Light intensity, in the visible wavelengths (in nanometers): 450, 500, 550, 570, 600, 650<\/strong><\/p><p>The visible light intensity is measured in microwatts per centimeters squared, with error bars of +\/- 12% of the value. The sensor selects the specific wavelength bands by using a set of silicon thin-film interference filters, to a precision of +\/- 5 nanometers. The bands are centered around the wavelengths listed above, and the bandwidth of each band is +\/- 20 nanometers full-width half-maximum around the band center, in a Gaussian distribution of sensitivity. Silicon is a hard material with low thermal expansivity, so the sensor characteristics are stable over a broad temperature range, as well as over the life of the sensor. The sensor\u2019s field of view is cone-shaped, with a cone angle of +\/- 20\u00b0 for a total field of view of 40\u00b0.<\/p><p><strong>STELLA-Q, 1.0, 1.1 and 2.0 \u2013 Light intensity (in microwatts per centimeters squared), in the near infrared wavelengths (in nanometers): 610, 680, 730, 760, 810, 860<\/strong><\/p><p>The near infrared light intensity is measured in microwatts per centimeters squared, with error bars of +\/- 12% of the value. The sensor selects the specific wavelength bands by using a set of silicon thin-film interference filters, to a precision of +\/- 5 nanometers. The bands are centered around the wavelengths listed above, and the bandwidth of each band is +\/- 10 nanometers full-width half-maximum around the band center, in a Gaussian distribution of sensitivity. Silicon is a hard material with low thermal expansivity, so the sensor characteristics are stable over a broad temperature range, as well as over the life of the sensor. The sensor\u2019s field of view is cone-shaped, with a cone angle of +\/- 20\u00b0 for a total field of view of 40\u00b0.<\/p><p><strong>STELLA-1.0, 1.1 and 2.0<\/strong> \u2013 Surface temperature, in degrees Celsius. This sensor measures a far infrared light spectrum to produce a spectral curve. This curve is fit to a black-body thermal emission curve, to derive the surface temperature. This sensor is calibrated to objects that are emissive (not shiny metal surfaces). The temperature reading is good to +\/- 0.5\u00b0C. The sensor\u2019s field of view is cone-shaped, with a cone angle of +\/- 17.5\u00b0, for a total field of view of 35\u00b0.<\/p><p><strong>STELLA-1.0, 1.1 and 2.0<\/strong> \u2013 Air temperature, in degrees Celsius. This sensor measures the ambient air temperature to an accuracy of +\/- 0.25\u00b0C. It measures the semiconductor conduction-band quantum energy band-gap to derive the temperature. This method of measurement is accurate across a wide range of temperatures (-40 to +125\u00b0C) and is stable over the life of the sensor.<\/p><p><strong>STELLA-1.0, 1.1 and 2.0<\/strong> \u2013 Ambient conditions: Relative humidity, barometric pressure, altitude, and air temperature. This sensor measures those four parameters, though the air temperature measurement is less accurate than that of the MCP9808, so we do not record this sensor\u2019s air temperature reading. The relative humidity measurement is good to +\/- 3% and the barometric pressure reading, in hectoPascals, is good to +\/-1 hPa. The altitude measurement is uncalibrated, so the absolute value is not accurate. The precision of the altitude measurement is better than 0.1%, so we include it to allow data marking by altitude excursion (a quick rise and fall) if the STELLA is in use on an aerial drone. In this way, the drone data and the STELLA data can be synchronized.<\/p><p><strong>All STELLAs<\/strong> \u2013 Time. The clock on the STELLA is set to Coordinated Universal Time (UTC) to avoid confusion of time zones and daylight savings time. The clock is powered by the backup battery and will continue to keep time, even when the STELLA is off. The accuracy of this clock chip is +\/- 2 seconds per day, about +\/- 12 minutes per year.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div id=\"e-n-tab-content-2644065124\" role=\"tabpanel\" aria-labelledby=\"e-n-tab-title-2644065124\" data-tab-index=\"4\" style=\"--n-tabs-title-order: 4;\" class=\" elementor-element elementor-element-c9744b1 e-con-full e-flex e-con e-child\" data-id=\"c9744b1\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-8c0812f elementor-widget elementor-widget-heading\" data-id=\"8c0812f\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Calibration Q &amp; A<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-06e16f3 elementor-widget elementor-widget-heading\" data-id=\"06e16f3\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h4 class=\"elementor-heading-title elementor-size-default\">Jesse Barber, STELLA Calibration and Validation\u200b<\/h4>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-ca9929a e-flex e-con-boxed e-con e-child\" data-id=\"ca9929a\" data-element_type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-5905331 elementor-widget elementor-widget-heading\" data-id=\"5905331\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">How do we calibrate our sensors?\u200b<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-f36796c elementor-widget elementor-widget-text-editor\" data-id=\"f36796c\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>We calibrate our sensors radiometrically, which means that we use a broadband light source that is well defined as to how much power per unit wavelength per unit area is coming off of the source. Knowing how the source behaves, we can then look at our sensor and see how it\u2019s data is different. We can then, after taking the measurement and gathering data, use a correction table to adjust the data coming off of the sensor to match what our source claims.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-774847b elementor-widget elementor-widget-heading\" data-id=\"774847b\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">Why do we need calibration?<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-39aec4b e-flex e-con-boxed e-con e-child\" data-id=\"39aec4b\" data-element_type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t<div class=\"elementor-element elementor-element-ce6233c e-con-full e-flex e-con e-child\" data-id=\"ce6233c\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-e832b03 elementor-widget elementor-widget-text-editor\" data-id=\"e832b03\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>We calibrate our sensors for a few reasons,<\/p><p>1: We cant be sure exactly how the sensors react to stimuli out of the factory. Each batch of silicon will be slightly different, leading to sensors built from year to year possibly having a different signature. We calibrate against a known source to make sure that the sensors are within factory calibrations and error bounds. And even if they are not, we then create a new set of data so that we understand by how far off the stellas could be from each other and the true value. This set of error data can then inform those who do not have our calibration equipment how far off their data might be from the truth.<\/p><p>2: Sensors and technology changes and degrades over time. Calibration against a source that is very well understood over years can tell us how long stellas might last without any calibration. And how to adjust for the drift over the years.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-1d2c547 e-con-full e-flex e-con e-child\" data-id=\"1d2c547\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-f3611c0 elementor-widget elementor-widget-image\" data-id=\"f3611c0\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t<figure class=\"wp-caption\">\n\t\t\t\t\t\t\t\t\t\t\t<a href=\"https:\/\/science.gsfc.nasa.gov\/stella\/\/wp-content\/uploads\/2025\/05\/Calibration_setup-scaled.jpg\" data-elementor-open-lightbox=\"yes\" data-elementor-lightbox-title=\"Calibration_setup\" data-e-action-hash=\"#elementor-action%3Aaction%3Dlightbox%26settings%3DeyJpZCI6MTIxMCwidXJsIjoiaHR0cHM6XC9cL3NjaWVuY2UuZ3NmYy5uYXNhLmdvdlwvc3RlbGxhXC93cC1jb250ZW50XC91cGxvYWRzXC8yMDI1XC8wNVwvQ2FsaWJyYXRpb25fc2V0dXAtc2NhbGVkLmpwZyJ9\">\n\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"843\" height=\"843\" src=\"https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/Calibration_setup-1024x1024.jpg\" class=\"attachment-large size-large wp-image-1210\" alt=\"Calibration Setup\" srcset=\"https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/Calibration_setup-1024x1024.jpg 1024w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/Calibration_setup-300x300.jpg 300w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/Calibration_setup-150x150.jpg 150w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/Calibration_setup-768x768.jpg 768w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/Calibration_setup-1536x1536.jpg 1536w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/Calibration_setup-2048x2048.jpg 2048w\" sizes=\"(max-width: 843px) 100vw, 843px\" \/>\t\t\t\t\t\t\t\t<\/a>\n\t\t\t\t\t\t\t\t\t\t\t<figcaption class=\"widget-image-caption wp-caption-text\">Early setup with calibration sphere and original STELLA<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-1bd456a elementor-widget elementor-widget-heading\" data-id=\"1bd456a\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">What set up do you use?\u200b<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-24c3e53 e-flex e-con-boxed e-con e-child\" data-id=\"24c3e53\" data-element_type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t<div class=\"elementor-element elementor-element-a081ba4 e-con-full e-flex e-con e-child\" data-id=\"a081ba4\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-cbe1c69 elementor-widget elementor-widget-text-editor\" data-id=\"cbe1c69\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>I use a LabSphere 12 in integrating sphere as my source. This produces a very even, diffuse circle of light 4\u201d in diameter. In one calibration test, I turn on the lamps in my sphere and look directly into the light. This is the most accurate and repeatable calibration test.<br \/><br \/>In another I add a diffusely reflective matte white panel into the system, and have the light from my sphere reflect off of the panel and into the sensor. This angle of reflection is as small as possible without the sensor casting a shadow on the panel.<br \/><br \/>In the final calibration test I take my panel, and replace it with a piece of sanded, white foam board. My panel is a laboratory grade surface that is 99% reflective from 350nm to 2500 nm. The foam is from a craft store. We do this to attempt to allow for those customers\/users to be able to calibrate a stella on their own at a low cost. And hopefully less than a 5-8% error compared to our lab grade equipment in the range that Stella operates.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-7289783 e-con-full e-flex e-con e-child\" data-id=\"7289783\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-f382a69 elementor-widget elementor-widget-image\" data-id=\"f382a69\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"576\" height=\"1024\" src=\"https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/CalibrationDiagram-1_v2-576x1024.png\" class=\"attachment-large size-large wp-image-1214\" alt=\"\" srcset=\"https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/CalibrationDiagram-1_v2-576x1024.png 576w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/CalibrationDiagram-1_v2-169x300.png 169w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/CalibrationDiagram-1_v2-768x1365.png 768w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/CalibrationDiagram-1_v2-864x1536.png 864w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/CalibrationDiagram-1_v2.png 1080w\" sizes=\"(max-width: 576px) 100vw, 576px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-cecdc82 elementor-widget elementor-widget-heading\" data-id=\"cecdc82\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">What variables do we try and control for?<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-01d847b elementor-widget elementor-widget-text-editor\" data-id=\"01d847b\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>We try to control how much light gets into the sensors, at what angle it enters the sensors, the distance at which the sensor sits from the source, and the humidity in the air to\u00a0 name a few. All of these, not including humidity, will change the resulting reading systematically, effecting the calibration. Humidity only effects one band in the infrared, but it is still good to control for.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-e5b5f45 elementor-widget elementor-widget-heading\" data-id=\"e5b5f45\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">What variables can\u2019t we control?<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-553b3ee e-con-full e-flex e-con e-child\" data-id=\"553b3ee\" data-element_type=\"container\">\n\t\t<div class=\"elementor-element elementor-element-d876747 e-con-full e-flex e-con e-child\" data-id=\"d876747\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-d408aab elementor-widget elementor-widget-text-editor\" data-id=\"d408aab\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>We cant control how each sensor comes from the factory, so any defects that get past quality control could change our data values by some percentage.<\/p><p>In most cases, this deviation is going to be within the factory\u2019s calibration error bounds and will not effect most customers, but it is important to know when we have a deviation from the norm.<\/p><p>We also cant control how sensors will behave over time, and so we have to observe them and correct for them.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-62d9f6d e-con-full e-flex e-con e-child\" data-id=\"62d9f6d\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-fbf8f69 elementor-widget elementor-widget-image\" data-id=\"fbf8f69\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"576\" height=\"1024\" src=\"https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/CalibrationDiagram-2-TALL-576x1024.png\" class=\"attachment-large size-large wp-image-1215\" alt=\"\" srcset=\"https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/CalibrationDiagram-2-TALL-576x1024.png 576w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/CalibrationDiagram-2-TALL-169x300.png 169w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/CalibrationDiagram-2-TALL-768x1365.png 768w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/CalibrationDiagram-2-TALL-864x1536.png 864w, https:\/\/science.gsfc.nasa.gov\/stella\/wp-content\/uploads\/2025\/05\/CalibrationDiagram-2-TALL.png 1080w\" sizes=\"(max-width: 576px) 100vw, 576px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-11672cc e-con-full e-flex e-con e-child\" data-id=\"11672cc\" data-element_type=\"container\">\n\t\t<div class=\"elementor-element elementor-element-45f2089 e-con-full e-flex e-con e-child\" data-id=\"45f2089\" data-element_type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-dcc9b4e elementor-widget elementor-widget-heading\" data-id=\"dcc9b4e\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">Why is it important to continue to check our calibration?<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-e67da0f elementor-widget elementor-widget-text-editor\" data-id=\"e67da0f\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>Sensor performance can degrade and change over time. So we calibrate at regular intervals with the same sensors to see how the sensors change and can inform our customers\/users.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-349f0e1 elementor-widget elementor-widget-heading\" data-id=\"349f0e1\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Julia Barsi, Landsat Radiometric Calibration Analyst\nGLAMR Science Manager\u200b<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-898a16b elementor-widget elementor-widget-heading\" data-id=\"898a16b\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">How do we calibrate our sensors?<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-bed0120 elementor-widget elementor-widget-text-editor\" data-id=\"bed0120\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>In the laboratory, calibration is usually performed in a controlled environment with a known reference target that is very well understood.\u00a0 Targets for the visible and near-infrared regions of the spectrum include diffuser panels and integrating spheres that have known reflectances which are illuminated with lamps or lasers that have known emitted radiances.\u00a0 Targets for the thermal region of the spectrum are usually blackbodies which emit a very stable temperature.\u00a0 The reference targets are generally very flat, so the sensor sees nothing but a uniform field.<\/p><p>The sensor is looks at the target, which generates some electronic response.\u00a0 The response is recorded along with the property of the reference target.\u00a0 The ratio of the sensor response to the target property is the radiometric calibration of the sensor.\u00a0<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-6401d4a elementor-widget elementor-widget-heading\" data-id=\"6401d4a\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">Why do we need calibration?<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-ad973ae elementor-widget elementor-widget-text-editor\" data-id=\"ad973ae\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>We need calibration to be able to make quantitative assessments of the physical properties being measured.\u00a0 The calibration allows us to convert the electronic signal (<em>current or voltage?) <\/em>in the STELLA instrument to the light intensity (microwatts per centimeter squared) or temperature (degrees Celsius).\u00a0 The calibration puts an absolute scale on the measurement that then can be quantitatively compared to other measurements.<\/p><p>Without calibration, we might be able to say that one plant is greener than another plant, for instance.\u00a0 But with calibration, we can say exactly how much greener one plant is and perhaps build a model of how greenness indicates plant health, for example.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-65afdd5 elementor-widget elementor-widget-heading\" data-id=\"65afdd5\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">What variables do we try and control for?<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-d9e7922 elementor-widget elementor-widget-text-editor\" data-id=\"d9e7922\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>Calibration is usually performed in a controlled environment to ensure that the sensor is only responding the physical input under test and not outside influences. \u00a0The internal temperature of the sensor may impact its responsiveness so it would be important to calibrate the sensor at the range of temperature conditions under which it would be used.\u00a0 The illumination conditions are generally controlled so that only light coming from the reference target is shining on the sensor.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-2d173f2 elementor-widget elementor-widget-heading\" data-id=\"2d173f2\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">Why is it important to continue to check our calibration?<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-17b913c elementor-widget elementor-widget-text-editor\" data-id=\"17b913c\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>Sensors can change over time.\u00a0 Sometimes a film builds up on mirrors or lenses making the optical path less transmissive.\u00a0 Sometimes the detector material degrades which causes loss of responsiveness. These changes can happen slowly or they can happen suddenly.\u00a0 And they will change the relationship between the sensor response and the physical parameter.\u00a0 If the calibration is not checked, the sensor response may have changed, but the result is that the physical property being measured appears to have changed.<\/p><p>For example, if the optical path has become 25% less transmissive, the sensor will be 25% less responsive.\u00a0 Let\u2019s say you measured a target at the beginning of the month that has a light intensity of 4 uW\/cm2 and you repeat the measurement at the end of the month but now is it only 3 uW\/cm2.\u00a0 With calibration, you would have known that the target would look 25% dark, but without calibration, you think the plant is less healthly.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"<p>Spectral Instruments About STELLA Spectrometers A Note About STELLA Data The performance of STELLA has not been scientifically peer-reviewed. STELLA spectrometers provide users the ability&hellip;<\/p>\n","protected":false},"author":2,"featured_media":1211,"parent":291,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_lmt_disableupdate":"no","_lmt_disable":"","footnotes":""},"class_list":["post-888","page","type-page","status-publish","has-post-thumbnail","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v25.4 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Spectral - STELLA<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/science.gsfc.nasa.gov\/stella\/instruments\/spectral\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Spectral - STELLA\" \/>\n<meta property=\"og:description\" content=\"Spectral Instruments About STELLA Spectrometers A Note About STELLA Data The performance of STELLA has not been scientifically peer-reviewed. 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