Research Page
Radiative Transfer
The Sun is a distant source of energy that reaches the Earth as spectrally rich solar radiation. The solar radiation relevant to Earth’s climate consists of ultra-violet radiation largely absorbed by stratospheric ozone, visible radiation to which the atmosphere is mostly transparent, and near-infrared and solar infrared radiation where some absorption by atmospheric water vapor occurs. In addition to solar radiation, the spectral region of longer-wavelength thermal-infrared radiation coming from terrestrial sources (the Earth’s surface and atmosphere) is equally important for weather and climate. Scientists in the Climate and Radiation Lab (CRL) study the individual spectral regions of solar and thermal radiation as well as the propagation of total (also known as “broadband”) shortwave and longwave fluxes to better understand the Earth’s radiation budget. The total solar flux across all wavelengths reaching the Earth is ≈ 1361 Wm-2, a number that has an important implication for the energy balance in Earth’s climate. Its slight variations are monitored as continuously and accurately as possible from space by missions such as the past SOlar Radiation and Climate Experiment (SORCE), and the recent Total and Spectral Solar Irradiance Sensor (TSIS) in which CRL has an overall responsibility for project science management.
The goal of solar radiation transport studies is to track the fate of the radiant energy entering at the top of the Earth’s atmosphere. The radiation can be either reflected back to space (with clouds playing a critical role in this mechanism), transmitted to the surface (where it is either absorbed or reflected) or absorbed by one of many atmospheric constituents (that can be either in gaseous, liquid or solid phase). This process of energy-driven computation also comprises the modeling of signals of a variety of so-called “passive” sensors which is the basis of physics-based atmospheric remote sensing in the solar and thermal IR spectra. Climate and Radiation Lab radiation scientists use many types of radiation observations for their studies: reflected and emitted to space measured by satellite instruments (e.g. MODIS, VIIRS, EPIC, AIRS, CERES, etc); transmitted and emitted towards the surface, using ground-based measurements (SMARTLabs); and absorbed, using simultaneous collocated satellites and ground observations and even aircraft measurements.
Computational tools called radiative transfer models assist in unearthing how such observations are connected through the properties of the Earth’s surface and atmosphere and interpret the radiation signals. The CRL is very active in the development of these tools. For effective and reliable simulation of the atmospheric radiation processes, the models should be computationally fast, yet theoretically well-grounded. Some of the radiation models co-developed by CRL scientists are publicly available and have thousands of users around the world. One example is the widely-used Mie scattering code to calculate accurate extinction and scattering characteristics of spherical particles. Another is the DISORT (Discrete Ordinates Radiative Transfer) code for radiative transfer in a multi-layered plane-parallel media, one of the most widely used codes in the atmospheric radiation community that continues to be refined by CRL staff. Recently, a Monte Carlo radiative transfer model supported by CRL scientists became publicly available as an open-source tool for studying radiative transfer in three-dimensional atmospheres and for intercomparing 3D radiative transfer codes. The development of so called “vectorized” radiation codes capable of simulating polarized atmospheric radiation is also an area of CRL expertise with potential for operational use in remote sensing applications in the very near future. Finally, CRL scientists have great interest in how approximate broadband radiative transfer codes used in Global Climate Models perform and have led initiatives (CIRC) to test the performance of such codes against more accurate (but less computationally efficient) standards.
Contact: Alexander Marshak
The goal of solar radiation transport studies is to track the fate of the radiant energy entering at the top of the Earth’s atmosphere. The radiation can be either reflected back to space (with clouds playing a critical role in this mechanism), transmitted to the surface (where it is either absorbed or reflected) or absorbed by one of many atmospheric constituents (that can be either in gaseous, liquid or solid phase). This process of energy-driven computation also comprises the modeling of signals of a variety of so-called “passive” sensors which is the basis of physics-based atmospheric remote sensing in the solar and thermal IR spectra. Climate and Radiation Lab radiation scientists use many types of radiation observations for their studies: reflected and emitted to space measured by satellite instruments (e.g. MODIS, VIIRS, EPIC, AIRS, CERES, etc); transmitted and emitted towards the surface, using ground-based measurements (SMARTLabs); and absorbed, using simultaneous collocated satellites and ground observations and even aircraft measurements.
Computational tools called radiative transfer models assist in unearthing how such observations are connected through the properties of the Earth’s surface and atmosphere and interpret the radiation signals. The CRL is very active in the development of these tools. For effective and reliable simulation of the atmospheric radiation processes, the models should be computationally fast, yet theoretically well-grounded. Some of the radiation models co-developed by CRL scientists are publicly available and have thousands of users around the world. One example is the widely-used Mie scattering code to calculate accurate extinction and scattering characteristics of spherical particles. Another is the DISORT (Discrete Ordinates Radiative Transfer) code for radiative transfer in a multi-layered plane-parallel media, one of the most widely used codes in the atmospheric radiation community that continues to be refined by CRL staff. Recently, a Monte Carlo radiative transfer model supported by CRL scientists became publicly available as an open-source tool for studying radiative transfer in three-dimensional atmospheres and for intercomparing 3D radiative transfer codes. The development of so called “vectorized” radiation codes capable of simulating polarized atmospheric radiation is also an area of CRL expertise with potential for operational use in remote sensing applications in the very near future. Finally, CRL scientists have great interest in how approximate broadband radiative transfer codes used in Global Climate Models perform and have led initiatives (CIRC) to test the performance of such codes against more accurate (but less computationally efficient) standards.
Contact: Alexander Marshak
