Sciences and Exploration Directorate

Kirk David Knobelspiesse


Kirk David Knobelspiesse's Contact Card & Information.
Phone: 301.614.6242
Org Code: 616
Mail Code 616.2
Greenbelt, MD 20771

Missions & Projects

Brief Bio

Dr. Kirk Knobelspiesse is a remote sensing specialist working to improve our ability to monitor the Earth’s climate. He has expertise in radiative transfer calculations, information content assessment, algorithm development, and validation with ground and airborne observations. Specific interests include polarimetric remote sensing of aerosols and clouds, atmospheric correction required for ocean color observations, and the statistical and AI tools useful for both.

Dr. Knobelspiesse received an undergraduate degree in Photography from the Rochester Institute of Technology in 1998, then a Master's degree in Imaging Science from the same university in 2000. For the next four years, he worked as a contractor at NASA GSFC on the SeaWiFS and SIMBIOS projects, then returned to graduate school at Columbia University in 2004. His PhD, in Applied Mathematics, dealt with remote sensing retrievals of atmospheric aerosols from multi-angle polarimeters. During his studies, he spent his time at NASA GISS, and remained at that institution for a postdoctoral fellowship following graduation. He took a position at NASA Ames in 2012, and returned to NASA GSFC in 2016.

Current Projects

Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) Mission


PACE Project Science Team Polarimeter Lead

PACE Postlaunch Airborne Experiment (PACE-PAX) Mission Scientist

Atmosphere Observation System (AOS) mission (formerly known as ACCP)

Remote Sensing

Instrument Scientist (Polarimeter)

MOCMAC Project: MODIS Ocean Color with MISR Atmospheric Correction

Remote Sensing

Funded as part of the NASA 2017 announcement "The Science of TERRA, AQUA and SUOMI NPP"

Recent publication: Knobelspiesse, K., A. Ibrahim, B. Franz, S. Bailey, R. Levy, Z. Ahmad, J. Gales, M. Gao, M. Garay, S. Anderson, and O. Kalashnikova. 2021. "Analysis of simultaneous aerosol and ocean glint retrieval using multi-angle observations." Atmospheric Measurement Techniques, 14: 3233-3252 [10.5194/amt-14-3233-2021]

Statistical validation tools soapbox

Remote Sensing

I find frequent usage of statistically inappropriate metrics to validate the 'success' of a remote sensing result when compared to some reference validation data. An alternative I prefer is the Bland-Altman, or mean-difference, plot, with associated statistical metrics. To illustrate, I've created a notebook demonstrating this method: .

Ocean microplastic remote sensing

Remote Sensing

"Advancing Remote Sensing of Microplastics on the Surface Ocean", Principal Investigator: Heidi Dierssen, University of Connecticut

Other Professional Information

Media and outreach

PACE Atmospheric science video feature

NASA Curious Universe podcast

AGU Third Pod from the Sun podcast

NASA "People of PACE" feature

NASA PACE cloud and aerosol article

NASA PACE climate science article

Cosmos magazine article

NASA GSFC Engage panel discussion


PACE-PAX field campaign, September 2024, California. Mission scientist

ACEPOL field campaign, October-November, 2017, California, NASA ER-2 aircraft. In-field flight planning.

ORACLES field campaign, Walvis Bay, Namibia and São Tomé, São Tomé and Príncipe, NASA ER-2 and P-3 aircraft, 2016, 2017, 2018. Deployment of RSP (Research Scanning Polarimeter) instrument, algorithm development.  

PODEX field campaign, California, NASA ER-2 aircraft, 2013. Deployment of RSP instrument.

ARCTAS field campaign, Yellowknife, Canada, NASA B-200 aircraft, 2008. Deployment of RSP instrument. 

MILAGRO field campaign, Veracruz, Mexico, Jetstream-31 aircraft, 2006. Deployment of RSP instrument.

ALIVE field campaign, central Oklahoma, Jetstream-31 aircraft, 2005. Deployment of RSP instrument. 

CNR (Italy), western Mediterranean Sea, R/V Urania, 2002. Deployment of ship-based atmospheric Lidar, hand held and automated sun photometers. 

CalCOFI, coastal California, R/V New Horizon, 2001. Deployment of handheld sun photometers and general cruise scientific support.



Research Oceanographer

Ocean Ecology Laboratory, NASA Goddard Space Flight Center - Greenbelt, MD

May 2016 - Present

Physical Scientist

Atmospheric Science Branch, Earth Science Division, NASA Ames Research Center - Moffett Field, CA

2012 - 2016

Postdoctoral Fellow

NASA Goddard Institute for Space Studies - New York, NY

2011 - 2012

Advisor: Dr. Michael Mishchenko

Graduate research assistant

Columbia University / NASA Goddard Institute for Space Studies - New York, NY

2006 - 2010

Advisor: Dr. Brian Cairns


NASA Goddard Space Flight Center / Science Systems and Applications, Inc. - Greenbelt, MD

2000 - 2004

Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) Project
Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) Project


Ph.D., Applied Mathematics, Columbia University, New York, NY. Thesis title: “Atmospheric aerosol optical property retrieval with scanning polarimeters,” 2011

M.S., Applied Mathematics, Columbia University, New York, NY, 2007

M.S., Imaging Science, Rochester Institute of Technology, Rochester, NY, 2000

B.S., Imaging and Photographic Technology, Rochester Institute of Technology, Rochester, NY, 1998

Professional Service

American Geophysial Union Fall meeting session organizer, 2014-2019

Advancement of POLarimetric Observations (APOLO) conference organizer, 2002


National Science Foundation, Integrative Graduate Education and Research Traineeship, Fellow 2004-2009

National Aeronautics and Space Administration, Group Achievement awards for the SIMBIOS Project (2003), ARCTAS field campaign (2009), INTEX-B field campaign (2008) and ORACLES field campaign (2019).


Quantitative simulation of polarimetric instruments using radiative transfer simulations and Bayesian statistical methods for the remote sensing of aerosols and clouds

New Investigator Program - National Aeronautics and Space Administration - Awarded: 2014-01-01

Dates: 2014-01-01  - 2016-12-31

Joint MISR/MODIS ocean color atmospheric correction with a new algorithm that utilizes reflected sun glint

The Science of Aqua, Terra and Suomi NPP - National Aeronautics and Space Administration - Awarded: 2018-06-01

Dates: 2018-06-01  - 2021-06-01



2024. "Unifying radiative transfer models in computer graphics and remote sensing, Part II: A differentiable, polarimetric forward model and validation." Journal of Quantitative Spectroscopy and Radiative Transfer 315 108849 [10.1016/j.jqsrt.2023.108849] [Journal Article/Letter]

2024. "Unifying radiative transfer models in computer graphics and remote sensing, Part I: A survey." Journal of Quantitative Spectroscopy and Radiative Transfer 314 108847 [10.1016/j.jqsrt.2023.108847] [Journal Article/Letter]

2023. "Simultaneous retrieval of aerosol and ocean properties from PACE HARP2 with uncertainty assessment using cascading neural network radiative transfer models." Atmospheric Measurement Techniques 16 (23): [] [Journal Article/Letter]

2023. "Performance evaluation of three bio-optical models in aerosol and ocean color joint retrievals." Atmospheric Measurement Techniques 16 (23): 5749-5770 [10.5194/amt-16-5749-2023] [Journal Article/Letter]

2023. "Optimizing retrieval spaces of bio-optical models for remote sensing of ocean color." Applied Optics 62 (13): 3299 [10.1364/ao.484082] [Journal Article/Letter]

2023. "The impact and estimation of uncertainty correlation for multi-angle polarimetric remote sensing of aerosols and ocean color." Atmospheric Measurement Techniques 16 (8): 2067–2087 [] [Journal Article/Letter]

2023. "The CHROMA cloud-top pressure retrieval algorithm for the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) satellite mission." Atmospheric Measurement Techniques 16 (4): 969-996 [10.5194/amt-16-969-2023] [Journal Article/Letter]

2022. "Circular polarization in atmospheric aerosols." Atmospheric Chemistry and Physics 22 (20): 13581--13605 [10.5194/acp-22-13581-2022] [Journal Article/Letter]

2022. "Effective uncertainty quantification for multi-angle polarimetric aerosol remote sensing over ocean." Atmos. Meas. Tech. 15 (16): 4859–4879 [10.5194/amt-15-4859-2022] [Journal Article/Letter]

2022. "Optimal Estimation Framework for Ocean Color Atmospheric Correction and Pixel-level Uncertainty Quantification." Applied Optics Vol. 61 No. 20 [10.1364/ao.461861] [Journal Article/Letter]

2021. "Adaptive Data Screening for Multi-Angle Polarimetric Aerosol and Ocean Color Remote Sensing Accelerated by Deep Learning." Frontiers in Remote Sensing 2 [10.3389/frsen.2021.757832] [Journal Article/Letter]

2021. "Aerosol properties in cloudy environments from remote sensing observations: a review of the current state of knowledge." Bulletin of the American Meteorological Society 1-57 [10.1175/bams-d-20-0225.1] [Journal Article/Letter]

2021. "Efficient multi-angle polarimetric inversion of aerosols and oceancolor powered by a deep neural network forward model." Atmospheric Measurement Techniques 14 (6): 4083–4110 [] [Journal Article/Letter]

2021. "Analysis of simultaneous aerosol and ocean glint retrieval using multi-angle observations." Atmospheric Measurement Techniques 14 3233-3252 [10.5194/amt-14-3233-2021] [Journal Article/Letter]

2021. "An overview of the ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) project: aerosol-cloud-radiation interactions in the Southeast Atlantic basin." Atmospheric Chemistry and Physics [10.5194/acp-21-1507-2021] [Journal Article/Letter]

2021. "Atmospheric correction over the ocean for hyperspectral radiometers using multi-angle polarimetric retrievals." Optics Express 29 (3): 4504 [10.1364/oe.408467] [Journal Article/Letter]

2021. "In situ Mg/Ca measurements on foraminifera: comparison between Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA‐ICP‐MS) and Wavelength‐Dispersive X‐Ray Spectroscopy by electron probe microanalyzer (EPMA)." Geochemistry, Geophysics, Geosystems [10.1029/2020gc009449] [Journal Article/Letter]

2020. "The Aerosol Characterization from Polarimeter and Lidar (ACEPOL) airborne field campaign." Earth System Science Data 12 (3): 2183-2208 [Full Text] [10.5194/essd-12-2183-2020] [Journal Article/Letter]

2020. "Inversion of multiangular polarimetric measurements from the ACEPOL campaign: an application of improving aerosol property and hyperspectral ocean color retrievals." Atmospheric Measurement Techniques 13 3939–3956 [10.5194/amt-13-3939-2020] [Journal Article/Letter]

2020. "Low-level liquid cloud properties during ORACLES retrieved using airborne polarimetric measurements and a neural network algorithm." Atmospheric Measurement Techniques 13 3447-3470 [10.5194/amt-13-3447-2020] [Journal Article/Letter]

2020. "Aerosol retrievals from different polarimeters during the ACEPOL campaign using a common retrieval algorithm." Atmospheric Measurement Techniques 13 553-573 [10.5194/amt-13-553-2020] [Journal Article/Letter]

2019. "How should we aggregate data? Methods accounting for the numerical distributions, with an assessment of aerosol optical depth." Atmospheric Chemistry and Physics 19 15023-15048 [10.5194/acp-19-15023-2019] [Journal Article/Letter]

2019. "Atmospheric Correction of Satellite Ocean-Color Imagery During the PACE Era." Frontiers in Earth Science 7 [10.3389/feart.2019.00145] [Journal Article/Letter]

2019. "Retrieving Aerosol Characteristics From the PACE Mission, Part 2: Multi-Angle and Polarimetry." Frontiers in Environmental Science 7 [10.3389/fenvs.2019.00094] [Journal Article/Letter]

2019. "Retrieving Aerosol Characteristics From the PACE Mission, Part 1: Ocean Color Instrument." Frontiers in Earth Science 7 [10.3389/feart.2019.00152] [Journal Article/Letter]

2019. "SPEX airborne spectropolarimeter calibration and performance." Applied Optics 58 (21): 5695 [10.1364/ao.58.005695] [Journal Article/Letter]

2019. "Inversion of multi-angular polarimetric measurements over open and coastal ocean waters: a joint retrieval algorithm for aerosol and water leaving radiance properties." Atmospheric Measurement Techniques 12 (7): 3921–3941 [10.5194/amt-12-3921-2019] [Journal Article/Letter]

2019. "Going Beyond Standard Ocean Color Observations: Lidar and Polarimetry." Frontiers in Marine Science 6 [10.3389/fmars.2019.00251] [Journal Article/Letter]

2019. "The Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission: Status, science, advances." Bulletin of the American Meteorological Society 100 (9): 1775–1794 [10.1175/bams-d-18-0056.1] [Journal Article/Letter]

2019. "Polarimetric remote sensing of atmospheric aerosols: Instruments, methodologies, results, and perspectives." Journal of Quantitative Spectroscopy and Radiative Transfer 224 474-511 [10.1016/j.jqsrt.2018.11.024] [Journal Article/Letter]

2019. "Intercomparison of airborne multi-angle polarimeter observations from the Polarimeter Definition Experiment." Applied Optics 58 (3): 650 [10.1364/ao.58.000650] [Journal Article/Letter]

2018. "Harnessing remote sensing to address critical science questions on ocean-atmosphere interactions." Elem Sci Anth 6 [10.1525/elementa.331] [Journal Article/Letter]

2018. "Development of neural network retrievals of liquid cloud properties from multi-angle polarimetric observations." Journal of Quantitative Spectroscopy and Radiative Transfer 220 39-51 [10.1016/j.jqsrt.2018.08.030] [Journal Article/Letter]

2018. "Remote sensing of aerosols with small satellites in formation flight." Atmospheric Measurement Techniques 11 (7): 3935-3954 [10.5194/amt-11-3935-2018] [Journal Article/Letter]

2018. "Comparisons of bispectral and polarimetric retrievals of marine boundary layer cloud microphysics: case studies using a LES–satellite retrieval simulator." Atmospheric Measurement Techniques 11 (6): 3689-3715 [10.5194/amt-11-3689-2018] [Journal Article/Letter]

2018. "Calibration and validation of Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) polarization measurements." Applied Optics 57 (16): 4499 [10.1364/ao.57.004499] [Journal Article/Letter]

2018. "Retrieval of aerosol properties and water-leaving reflectance from multi-angular polarimetric measurements over coastal waters." Optics Express 26 (7): 8968 [10.1364/oe.26.008968] [Journal Article/Letter]

2018. "Atmospheric correction for hyperspectral ocean color retrieval with application to the Hyperspectral Imager for the Coastal Ocean (HICO)." Remote Sensing of Environment 204 60-75 [10.1016/j.rse.2017.10.041] [Journal Article/Letter]

2017. "Water-leaving contribution to polarized radiation field over ocean." Optics Express 25 (16): A689 [10.1364/oe.25.00a689] [Journal Article/Letter]

2016. "Information content and sensitivity of the 3β + 2α lidar measurement system for aerosol microphysical retrievals." Atmospheric Measurement Techniques 9 (11): 5555-5574 [10.5194/amt-9-5555-2016] [Journal Article/Letter]

2015. "Cloud thermodynamic phase detection with polarimetrically sensitive passive sky radiometers." Atmos. Meas. Tech 8 1537-1554 [10.5194/amt-8-1537-2015] [Journal Article/Letter]

2015. "Liquid water cloud properties during the Polarimeter Definition Experiment (PODEX)." Remote Sens. Environ. 169 20-36 [doi:10.1016/j.rse.2015.07.029] [Journal Article/Letter]

2014. "Remote sensing of above cloud aerosols." Light Scattering Reviews 9 167-210 [Article in Book]

2014. "A multiparameter aerosol classification method and its application to retrievals from spaceborne polarimetry." J. Geophys. Res. Atmos. 119 (16): 9838–9863 [10.1002/2013JD021411] [Journal Article/Letter]

2013. "Information content of aerosol retrievals in the sunglint region." Geophys. Res. Lett. 40 (3): 631-634 [10.1002/grl.50148] [Journal Article/Letter]

2013. "Uncertainty and interpretation of aerosol remote sensing due to vertical inhomogeneity." J Quant Spectrosc Radiat Transfer 114 91-100 [10.1016/j.jqsrt.2012.08.006] [Journal Article/Letter]

2012. "Polarimetric retrievals of surface and cirrus clouds properties in the region affected by the Deepwater Horizon oil spill." Remote Sens Environ 121 389-403 [10.1016/j.rse.2012.02.016] [Journal Article/Letter]

2012. "Analysis of fine-mode aerosol retrieval capabilities by different passive remote sensing instrument designs." Opt. Express 20 (19): 21,457-21,484 [10.1364/OE.20.021457] [Journal Article/Letter]

2012. "Sensitivity of multiangle, multispectral polarimetric remote sensing over open oceans to water-leaving radiance: Analyses of RSP data acquired during the MILAGRO campaign." Remote Sens Environ 118 284-308 [10.1016/j.rse.2011.11.003] [Journal Article/Letter]

2011. "Simultaneous retrieval of aerosol and cloud properties during the MILAGRO field campaign." Atmos. Chem. Phys. 11 (13): 6245-6263 [10.5194/acp-11-6245-2011] [Journal Article/Letter]

2011. "Combined retrievals of boreal forest fire aerosol properties with a polarimeter and lidar." Atmos. Chem. Phys. 11 (14): 7045-7067 [10.5194/acp-11-7045-2011] [Journal Article/Letter]

2009. "Polarimetric remote sensing of aerosols over land." J. Geophys. Res. 114 (D1): D01206 [10.1029/2008JD010619] [Journal Article/Letter]

2008. "Surface BRDF estimation from an aircraft compared to MODIS and ground estimates at the Southern Great Plains site." J. Geophys. Res. 113 (D20): D20105 [10.1029/2008JD010062] [Journal Article/Letter]

2005. "Evaluation of aerosol properties over ocean from Moderate Resolution Imaging Spectroradiometer (MODIS) during ACE-Asia." J. Geophys. Res. 110 (D7): D07308 [10.1029/2004JD005208] [Journal Article/Letter]

2005. "Study of the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) aerosol optical property data over ocean in combination with the ocean color products." J. Geophys. Res. 110 (D10): D10S06 [10.1029/2004JD004950] [Journal Article/Letter]

2005. "Analysis of shipboard aerosol optical thickness measurements from multiple sunphotometers aboard the R/V Ronald H. Brown during the Aerosol Characterization Experiment - Asia." Applied Optics 44 (18): 3805 [10.1364/AO.44.003805] [Journal Article/Letter]

2004. "Maritime aerosol optical thickness measured by handheld sun photometers." Remote Sensing of Environment 93 (1-2): 87-106 [10.1016/j.rse.2004.06.018] [Journal Article/Letter]

2003. "Unique data repository facilitates ocean color satellite validation." Eos, Transactions American Geophysical Union 84 (38): 377 [10.1029/2003EO380001] [Journal Article/Letter]

2003. "Sun-Pointing Error Correction for Sea Deployment of the MICROTOPS II Handheld Sun Photometer." J Atmos Ocean Tech 20 (5): 767-772. [Journal Article/Letter]

2003. "Investigation of Ocean Color Atmospheric Correction Algorithms Using In Situ Measurements of Aerosol Optical Thickness: Application to MODIS." NASA/TM-2003 41-46 [Article in Book]

2003. "Sun-Pointing-Error Correction for Sea Deployment of the MICROTOPS II Handheld Sun Photometer." J Atmos and Ocean Tech 20 (5): 767-771 [10.1175/1520-0426(2003)20<767:SPECFS>2.0.CO;2] [Journal Article/Letter]

2003. "Sun and Sky Radiance Measurements and Data Analysis Protocols." NASA/TM-2003-211621/Rev4-Vol III 60-78 [Article in Book]

2003. "Calibration of Sun Photometers and Sky Radiance Sensors." NASA/TM-2003-211621/Rev4-Vol II 34-49 [Article in Book]

2002. "Sun and Sky Radiance Measurements and Data Analysis Protocols." NASA Tech Memo 2002-210004 211-227 [Article in Book]

2002. "Calibration of Sun Photometers and Sky Radiance Sensors." NASA Tech Memo 2002-210004, Rev 3, Vol 1 76-90 [Article in Book]


2003. "SIMBIOS Project Data Processing and Analysis Results." NASA/TM-2003-211622 11841 [Article in Book]

2003. "Ocean Optics Protocols for Satellite Ocean Color Sensor Validation, Revision 4, Volume III: Radiometric Measurements and Data Analysis Protocols." NASA/TM-2003-211621/Rev4-Vol III 57 pp [Other]

2003. "Ocean Optics Protocols for Satellite Ocean Color Sensor Validation, Revision 4, Volume II: Instrument Specifications, Characterization, and Calibration." NASA/TM-2003-211621/Rev4-Vol II 57 pp [Other]

2003. "SIMBIOS Program in Support of Ocean Color Missions: 1997-2003." Proc SPIE Int Soc Opt Eng 5155 49-60 [Other]

2002. "Ocean Optics Potocols for Satellite Ocean Color Sensor Validation." NASA Tech Memo 2002-210004, Rev 3, Vol 1 iii-iv [Other]