[1] 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. The demonstration is based on a 21 November 2002 underflight of the AIRS on the NASA Aqua spacecraft by the Scanning-HIS on the NASA ER-2 high-altitude aircraft. A comparison technique which accounts for the different viewing geometries and spectral characteristics of the two sensors is introduced, and accurate comparisons are made for AIRS channels throughout the infrared spectrum. Resulting brightness temperature differences are found to be 0.2 K or less for most channels. Both the AIRS and the Scanning-HIS calibrations are expected to be very accurate (formal 3-sigma estimates are better than 1 K absolute brightness temperature for a wide range of scene temperatures), because high spectral resolution offers inherent advantages for absolute calibration and because they make use of high-emissivity cavity blackbodies as onboard radiometric references. AIRS also has the added advantage of a cold space view, and the Scanning-HIS calibration has recently benefited from the availability of a zenith view from high-altitude flights. 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, including those from the NASA EOS spacecraft (Terra, Aqua and Aura) and the new complement of NPOESS operational instruments. The validation role for accurately calibrated aircraft spectrometers also includes application to broadband instruments and linking the calibrations of similar instruments on different spacecraft. It is expected that aircraft flights of the Scanning-HIS and its close cousin the NPOESS Airborne Sounder Test Bed (NAST) will be used to check the long-term stability of AIRS and the NPOESS operational follow-on sounder, the Cross-track Infrared Sounder (CrIS), over the life of the missions.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2005JD006094

Radiometric and spectral validation of Atmospheric Infrared Sounder observations with the aircraft-based Scanning High-Resolution Interferometer Sounder

[1] The fundamental measurement of the Tropospheric Emission Spectrometer (TES) on board the Aura spacecraft is upwelling infrared spectral radiances. Accurate TES retrievals of surface and atmospheric parameters such as trace gas amounts critically depend on well-calibrated radiance spectra. On-orbit TES nadir observations were evaluated using carefully selected, nearly coincident spectral radiance measurements from Atmospheric Infrared Sounder (AIRS) on Aqua and special scanning high-resolution interferometer sounder (SHIS) underflights. Modifications to the L1B calibration algorithms for TES version 2 data resulted in significant improvements for the TES-AIRS comparisons. The comparison of TES with SHIS (adjusted for geometric differences) show mean and standard deviation differences of less than 0.3 K at warmer brightness temperatures of 290–295 K. The TES/SHIS differences are less than 0.4 K at brightness temperatures of 265–270 K. There are larger TES/SHIS comparison differences for higher-frequency TES 1A1 filter, which has less upwelling radiance signal. The TES/AIRS comparisons show mean differences of less than 0.3 K at 290–295 K and less than 0.5 K at 265–270 K with standard deviation less than 0.6 K for the majority of the spectral regions and brightness temperature range. A procedure to warm up the optical bench for better alignment in December 2005 gave a fourfold increase in the signal-to-noise ratio at higher frequency ranges. Recent results from a long-term comparison of TES sea surface temperature (SST) observations with the Reynolds optimally interpolated (ROI) SST product demonstrates TES radiometric stability.

/pdf/tropospheric-emission-spectrometer-nadir-spectral-radiance-4mhcln9hxp.pdf

Tropospheric Emission Spectrometer nadir spectral radiance comparisons

This paper describes the theory and application of the minimum local emissivity variance (MLEV) technique for simultaneous retrieval of cloud pressure level and effective spectral emissivity from high-spectral-resolution radiances, for the case of single-layer clouds. This technique, which has become feasible only with the recent development of high-spectral-resolution satellite and airborne instruments, is shown to provide reliable cloud spectral emissivity and pressure level under a wide range of atmospheric conditions. The MLEV algorithm uses a physical approach in which the local variances of spectral cloud emissivity are calculated for a number of assumed or first-guess cloud pressure levels. The optimal solution for the single-layer cloud emissivity spectrum is that having the “minimum local emissivity variance” among the retrieved emissivity spectra associated with different first-guess cloud pressure levels. This is due to the fact that the absorption, reflection, and scattering processes...

Minimum Local Emissivity Variance Retrieval of Cloud Altitude and Effective Spectral Emissivity—Simulation and Initial Verification

Development in the mid 80s of the High-resolution Interferometer Sounder (HIS) instrument for the high altitude NASA ER2 aircraft demonstrated the capability for advanced atmospheric temperature and water vapor sounding and set the stage for new satellite instruments that are now becoming a reality [AIRS(2002), CrIS(2006), IASI(2006), GIFTS(200?), HES(2013)]. Follow-on developments at the University of Wisconsin that employ Fourier Transform Infrared (FTIR) for Earth observations include the ground-based Atmospheric Emitted Radiance Interferometer (AERI) and the new Scanning HIS aircraft instrument.
The Scanning HIS is a smaller version of the original HIS that uses cross-track scanning to enhance spatial coverage. Scanning HIS and its close cousin, the NPOESS Airborne Sounder Testbed (NAST), are being used for satellite instrument validation and for atmospheric research. A novel detector configuration on Scanning HIS allows the incorporation of a single focal plane and cooler with three or four spectral bands that view the same spot on the ground. The calibration accuracy of the S-HIS and results from recent field campaigns are presented, including validation comparisons with the NASA EOS infrared observations (AIRS and MODIS). 
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, including those from the NASA EOS spacecrafts (Terra, Aqua and Aura) and the new complement of NPOESS operational instruments. It is expected that aircraft flights of the S-HIS and the NAST will be used to check the long-term stability of AIRS and the NPOESS operational follow-on sounder, the Cross-track Infrared Sounder (CrIS), over the life of the mission.

http://library.ssec.wisc.edu/research_Resources/publications/pdfs/SPIE/Revercomb_SPIE_5655.pdf

Highly accurate FTIR observations from the Scanning HIS aircraft instrument

. The purpose of this scientific survey is to support the research being conducted at York University in the field of spectroscopy and nanosatellites using Argus 1000 micro- spectrometer and low cost unmanned aerial vehicle (UAV) system. On the CanX-2 mission, the Argus spectrometer observes reflected infrared solar radiation emitted by Earth surface targets as small as 1.5 km within the 0.9-1.7 μm range. However, limitations in the volume of data due to onboard power constraints and a lack of an onboard camera system make it very difficult to verify these objectives using ground truth. In the last five years that Argus has been in operation, we have made over 200 observations over a series of land and ocean targets. We have recently examined algorithms to improve the geolocation accuracy of the spectrometer payload and began to conduct an analysis of soil health content using Argus spectral data. A field campaign is used to obtain data to assess geolocation accuracy using coastline crossing detection and to obtain airborne bare soil spectra in ground truth form. The payload system used for the field campaign consists of an Argus spectrometer, optical camera, GPS, and attitude sensors, integrated into a low-cost, unmanned aerial vehicle (UAV), which will be presented along with the experimental procedure and field campaign results.

/pdf/remote-spectral-imaging-using-a-low-cost-uav-system-1nq7t2h7wq.pdf

Remote spectral imaging using a low cost uav system

Broadband IR high spectral resolution observations of atmospheric emission provide key meteorological information related to atmospheric state parameters, cloud and surface spectral properties, and processes influencing radiative budgets and regional climate. Fourier transform spectroscopy (FTS), or Michelson interferometry, has proven to be an exceptionally effective approach for making these IR spectral observations with the high radiometric accuracy necessary for weather and climate applications, and are currently developing a new airborne instrument for use on an unmanned aerospace vehicle (UAV). These include the high- resolution interferometer sounder aircraft instrument developed for the NASA high altitude ER2, the atmospheric emitted radiance interferometer (AERI) and the new AERI-UAV for application in the DOE atmospheric radiation measurement program. This paper focuses on the design of the AERI-UAV which is novel in many respects. The efforts will help speed the day when this valuable instrumentation is used to improve remote sensing and radiative budget observations from space.

Jean Giroux

Papers

Airborne and ground-based Fourier transform spectrometers for meteorology: HIS, AERI, and the new AERI-UAV