Steven Dutcher

Validation of Atmospheric InfraRed Sounder (AIRS) spectral radiances with the Scanning High-resolution Interferometer Sounder (S-HIS) aircraft instrument

The ability to accurately validate high spectral resolution infrared radiance measurements from space using comparisons with aircraft spectrometer observations has been successfully demonstrated. The demonstration is based on an under-flight of the Atmospheric Infrared Sounder (AIRS) on the NASA Aqua spacecraft by the Scanning High resolution Interferometer Sounder (S-HIS) on the NASA ER-2 high altitude aircraft on 21 November 2002 and resulted in brightness temperature differences approaching 0.1K for most of the spectrum. This paper presents the details of this AIRS/S-HIS validation case and also presents comparisons of Aqua AIRS and Moderate Resolution Imaging Spectroradiometer (MODIS) radiance observations. Aircraft comparisons of this type provide a mechanism for periodically testing the absolute calibration of spacecraft instruments with instrumentation for which the calibration can be carefully maintained on the ground. This capability is especially valuable for assuring the long-term consistency and accuracy of climate observations. It is expected that aircraft flights of the S-HIS and its close cousin the National Polar Orbiting Environmental Satellite System (NPOESS) Atmospheric Sounder Testbed (NAST) will be used to check the long-term stability of the NASA EOS spacecrafts (Terra, Aqua and Aura) and the follow-on complement of operational instruments, including the Cross-track Infrared Sounder (CrIS).

On-orbit absolute blackbody emissivity determination using the heated halo method

The Climate Absolute Radiance and Refractivity Observatory is a satellite mission that will measure the Earths outgoing spectral radiance with accuracy better than 0.1 K in radiance temperature for climate benchmarking and forecast testing. Part of the high-accuracy calibration system is the heated halo, which provides a robust and compact method to measure the spectral emissivity of a blackbody. Measurement of the combined radiance of a blackbody, the reflection from a thermal source, and knowledge of key temperatures and the viewing geometry allow the blackbody spectral emissivity to be calculated. This allows the determination of blackbody radiance, and thus calibration of the CLARREO instrument, with high accuracy.

Recent efforts to validate EOS observations: hyperspectral data noise characterization using PCA: application to AIRS

Exploiting the redundancy in high spectral resolution observations, dependent set Principle Component Analysis (PCA) is a simple yet very powerful tool not only for noise filtering and lossy compression, but also for the characterization of sensor noise and other variable artifacts using Earth scene data. Our approach for dependent set PCA of AIRS Earth scene data is presented. Aspects of the analyses include 1) estimation of NEDT using PCA and comparisons to values derived from on-board blackbodies, 2) estimation of the scene dependence of NEDN, 3) estimation of the spectrally correlated component of NEDT and comparison to pre-launch analyses using blackbody views, 4) investigation of non- Gaussian noise behavior, and 5) inspection of individual PCs. The results of the PCA analyses are generally consistent with results obtained pre-launch and on-orbit using blackbody and/or space view data. Specific findings include: 1) PCA estimates of AIRS spectrally random and spectrally correlated NEDN compare well with estimates computed from on-board blackbody and space views, 2) the signal dependence of AIRS NEDN is accurately parameterized in terms of the scene radiance, 3) examination of the reconstruction error allows non-Gaussian phenomenon such as popping to be characterized, and 4) inspection of the PCs and individual PC filtered radiance spectra is a powerful technique for diagnosing low level artifacts in hyperspectral data.

On-orbit Absolute Blackbody Emissivity Determination Using the Heated Halo Method

The Heated Halo method can be used to accurately measure the spectral emissivity of a blackbody, on-orbit, using a broadband thermal source.

Hyperspectral Sounding Measurements-Specification of CLARREO FOV Size

AIRS data are used to perform global hyperspectral atmospheric sounding retrievals for different horizontal resolutions (15 km - 100 km). The purpose of this research is to optimize the CLARREO field of view size specification.

Validation of AIRS cloud-cleared radiances using high spectral resolution infrared aircraft observations

This study will present results of an effort to validate the accuracy of the cloud-cleared radiance products of the Atmospheric Infrared Sounder (AIRS) using observations from a variety of aircraft based sensors. The AIRS cloud-clear radiances are a product of the Level 2 ground processing software developed by the NASA AIRS science team. The cloud-clear radiance represents an estimate of the infrared upwelling spectrum at the top of the atmosphere for a cloud free atmosphere. This study concentrates on observations collected during the Pacific THORpex experiment, conducted in February-March 2003. NASA ER-2 aircraft based observations from the Scanning-High Resolution Interferometer Sounder (S-HIS) and the MODIS Airborne Simulator (MAS) are used in this validation effort.

Techniques used in improving the radiance validation of Atmospheric Infrared Sounder (AIRS) observations with the Scanning High-Resolution Interferometer Sounder (S-HIS)

The ability to accurately validate high spectral resolution infrared radiance measurements from space using comparisons with a high altitude aircraft spectrometer has been successfully demonstrated (Tobin, et al. 2006). A comparison technique which accounts for the different viewing geometries and spectral characteristics of the two sensors was introduced, and accurate comparisons were made for AIRS channels throughout the infrared spectrum. Resulting brightness temperature differences were found to be 0.2 K or less for most channels. Continuing work on additional cases has shown some channels to have brightness temperature differences larger than 0.2 K. Atmospheric contribution from above the aircraft is a suspected factor in producing the larger differences. The contribution of upper atmosphere HNO3 and O3 are studied as contributors to the brightness temperature differences. Improved forward model calculations are used to understand and compensate for the above aircraft atmospheric contribution. Results of this effort to understand the observed temperature differences are presented. The methodology demonstrated for the NASA AIRS instrument is expected to be used in the validation of the CrIS sensor radiances from the operational NPP/NPOESS platforms and the IASI sensor radiances from the METOP platforms.

Performance of an infrared sounder on several airborne platforms: the Scanning High Resolution Interferometer Sounder (S-HIS)

A comparison of S-HIS instrument performance on various airborne platforms, and during ground characterization is presented. Specific emphasis is placed on instrument improvements, 1998 to present day, and the engineering lessons learned. Also discussed is the ability to accurately validate high spectral resolution IR radiance measurements from space using comparisons with aircraft spectrometer observations. Aircraft comparisons of this type provide a mechanism for periodically verifying expected absolute calibration of spacecraft instruments with instrumentation for which the calibration can be carefully maintained on the ground. This capability is especially valuable for achieving the long-term consistency and accuracy of climate observations, including those from the NASA EOS spacecrafts (Terra, Aqua, Aura).

FTS Calibration: Demonstrated Absolute Accuracy for IR Remote Sensing and Future for Monitoring Climate

Characterization of our airborne (Scanning High-resolution Interferometer Sounder, S-HIS) and ground-based (Atmospheric Emitted Radiance Interferometer, AERI) instruments illustrates state-of-the-art calibration performance. Application to validation of satellite radiances and to establishing climate reference observations is discussed.