AIRS Point Spread Function Reconstruction: Using AIRS and MODIS Data
No abstract provided
Vese, Luminita↗
Engineering topics
Manning, Evan M.
Publications and source records attributed to Manning, Evan M..
Causes and Effects of AIRS Optics Temperature Cycles
In addition to the expected orbital thermal cycle, geophysical conditions with high thermal and reflected upwelling infrared (IR) drive measurable changes in the AIRS instrument with a period of 24 hours. Especially hot and bright scenes are important, with about 30% of the variability driven by thermal IR and 70% by reflected IR. We show how these cycles manifest in the instrument telemetry for temperatures and gain and with careful analysis can even be detected in spectral shifts.Thermal cycles are an unavoidable feature of instruments observing upwelling radiances from Earth, because the signal inherently carries varying amounts of energy into the instrument. Temperature control of the optical bench, on-board calibrator blackbody, and Focal Plane Array (FPA) in AIRS reduce the impacts of temperature variability to extremely small levels. This combined with good on-board telemetry of the temperatures and including temperature variability in our calibration algorithm has resulted in an instrument that achieves ‘climate quality’ measurements. Careful instrument and algorithm design allows us to characterize and document the impact of temperature variability and limit the effects to negligible levels, helping the instrument meet important climate-quality criteria specified in Ohring 2005
Overoye, Kenneth↗
Improving the longest SI traceable hyperspectral infrared record from space: AIRS
UNKNOWN
Strow, Larrabee↗
Checking AIRS nonlinearity in flight
Radiances from the Atmospheric Infrared Sounder (AIRS) show excellent stability and are traceable to SI standards through the On-Board Calibrator (OBC) blackbody. The OBC can be used to check the nonlinearity by turning off the heater and letting the target float from 308K to roughly 261K while acquiring data. The OBC Float test was performed once prior to launch, and again shortly after launch. Until now, the OBC Float test did not produce accurate nonlinearity results.
Aumann, Hartmut↗
Radiometric Stability in 16 years of AIRS hyperspectral infrared data (SPIE OP-431-20)
UNKNOWN
Manning, Evan M.↗
Radiometric Stability in 16 years of AIRS Hyperspectral Infrared Data (SPIE OP-431-20)
With global warming at the rate of 10 mK/yr, it is important to at least characterize any trend in the AIRS data, which may impact the use of AIRS data for climate change research. We evaluated the stability of the AIRS v5 calibration for seven atmospheric window channels between 2002 and 2018 under tropical ocean clear conditions. Trends for the channels between 961, 1128 and 1231 cm-1 channels are typically +3 mK/yr; for 790 and 901 cm-1 the trend is 6 mK/yr, i.e. the observations are increasingly getting warmer than expected. The trends are day/night consistent. The trend for the 2508 and 2616 cm-1 channels is close to 10 mK/yr at night, but closer to 6 mK/yr during the day. On an absolute scale these trends are small, but not when viewed in the context of global warming at a 10 mK/yr rate. While the warming trends are consistent with increased scattering from the scan mirrors, which create an error in reading the Onboard Blackbody Calibration, the resulting changes in the gain are a factor of about five larger than observed changes in the gain. The effects of scattering due to scan mirror contamination are evident at extremely cold temperatures, but scattering does not produce the observed warming at warm temperatures. It is possible that much of the observed warming in the AIRS window channels is a geophysical effect related to the warming of the oceans, resulting in a shift in the diurnal cycle and skin effect correction. This requires more careful evaluation.
Manning, Evan M.↗
Radiometric Stability in 16 years of AIRS Hyperspectral Infrared Data (SPIE OP-431-20)
With global warming at the rate of 10 mK/yr, it is important to at least characterize any trend in the AIRS data, which may impact the use of AIRS data for climate change research. We evaluated the stability of the AIRS v5 calibration for seven atmospheric window channels between 2002 and 2018 under tropical ocean clear conditions. Trends for the channels between 961, 1128 and 1231 cm-1 channels are typically +3 mK/yr; for 790 and 901 cm-1 the trend is 6 mK/yr, i.e. the observations are increasingly getting warmer than expected. The trends are day/night consistent. The trend for the 2508 and 2616 cm-1 channels is close to 10 mK/yr at night, but closer to 6 mK/yr during the day. On an absolute scale these trends are small, but not when viewed in the context of global warming at a 10 mK/yr rate. While the warming trends are consistent with increased scattering from the scan mirrors, which create an error in reading the Onboard Blackbody Calibration, the resulting changes in the gain are a factor of about five larger than observed changes in the gain. The effects of scattering due to scan mirror contamination are evident at extremely cold temperatures, but scattering does not produce the observed warming at warm temperatures. It is possible that much of the observed warming in the AIRS window channels is a geophysical effect related to the warming of the oceans, resulting in a shift in the diurnal cycle and skin effect correction. This requires more careful evaluation.
Manning, Evan M.↗
Reducing Uncertainty in the AIRS Radiometric Calibration
The Atmospheric Infrared Sounder (AIRS) radiometric calibration coefficients convert the counts measured from the instruments A/D converters (Level 1A) to SI traceable radiance units (Level 1B). The calibration equations are based on how the instrument operates and follow a simple second order relationship between counts and radiance. Terms are included to account for nonlinearity of the detectors, emissivity and temperature knowledge of the on-board calibrator (OBC) blackbody and radiometric offset due to coupling of the polarization of the scan mirror with the spectrometer. In this paper, we re-derive the radiometric calibration equation with a little more rigor and account for the view angle of each of the 4 space views. We then derive new polarization coefficients from the 4 space views over the mission and use them re-derive the coefficients for blackbody emissivity and nonlinearity. We then compare new coefficients (Version 7k) with the latest operational version of the AIRS radiometric calibration coefficients (Version 5). The AIRS Version 5 coefficients were sufficiently adequate that an update has never been made since AIRS launch in 2002. However, it can be seen, when we compare to the Cross-track Infrared Sounder (CrIS), that better agreement is made in Version 7. The impact of the new coefficients is highest at cold scene temperatures and very warm temperatures.
Strow, Larrabee↗
Stratified Radiometric Means for the Evaluation of AIRS and CrIS
There are now five hyperspectral infrared sounders in orbit (AIRS, two CrIS instruments, two IASI instruments). A longterm record spanning these instruments and continuing forward with future instruments holds great promise for the study of weather and climate. This long-term record must separate the effects of instrument artifacts and weather variability. We introduce the “StratRad” stratified radiance means product, containing means of groups of spectra for AIRS on Aqua and CrIS on SNPP. We show how this product can be used both to illuminate instrument artifacts and to study common observations of weather patterns at an accuracy of better than 0.1 K. Radiances are stratified by latitude, longitude, day/night, land/sea, and observation angle.
Kahn, Brian H.↗
Hyperspectral Sounder Performance for Cold Scenes
We investigate the use of 200K scenes as a valuable “stress test” for the evaluation of the calibration of AIRS and CrIS. Under these conditions both instruments show artifacts much larger than the nominal stated radiometric accuracy of about 0.1-0.2 K. Except for the AIRS shortwave trend, both instruments clearly perform well at the 1 K level even for these extremely low scene temperatures. Unfortunately, changes in extremes, in this case cold extremes, are of great interest to the evaluation of climate change effects, such as changes in the height of the tropopause or the frequency of severe storms. The evaluation of the AIRS performance at extremely low scene temperatures has been key to identifying the need for updating the polarization coefficients in the L1B software Version 7. These changes are expected to eliminate a large fraction of the observed AIRS artifacts. The CrIS instrument teams is also working on refining the calibration.
Manning, Evan M.↗
Tropical SNO Comparisons of AIRS and CrIS Calibration for Windows
AIRS (Atmospheric Infrared Sounder) on EOS (Earth Observing System)-Aqua and CrIS (Cross-track Infrared Sounder) on Suomi NPP (National Polar-orbiting Partnership) are two hyperspectral infrared sounders with similar capabilities and orbits, so there is a great opportunity to compare their absolute calibration while they are both in orbit. This insures that long-term climate record can be created by concatenating the two instrument records. There are significant differences in instrument architecture which may lead to subtle differences and complicate attempts to combine the records. We use Tropical Simultaneous Nadir Observations (TSNOs), cases where both instruments are looking nearly at the same place at the same time, to explore the differences. Due to the presence of cold clouds and clear hot desert surface, the data cover a brightness temperature range from 190 degrees Kelvin to 340 degrees Kelvin. We concentrate on the differences between the mean of the two instruments using atmospheric window channels as function of brightness temperature in 20-degree-Kelvin wide bins. With the currently available AIRS and CrIS official calibrated data, radiometric differences as large as 0.3 degrees Kelvin are seen at the extreme temperatures. These differences may be reduced in future releases of the AIRS and CrIS calibration.
CrIS↗