Gao, Bo-Cai: Naval Research Laboratory (Project Lead)
Project Funding:
2017 - 2019
NRA: 2016 NASA: Utilization of Airborne Visible/Infrared Imaging Spectrometer- Next Generation Data from an Airborne Campaign in India-AVRSNG
Funded by NASA
Abstract:
During the airborne campaign conducted in India in late 2015 and early 2016, a huge amount of hyperspectral imaging data was collected with the AVIRISng imaging spectrometer from an aircraft for research in many areas, including agriculture and soils, wetland ecosystems, biological oceanography, coastal land use/land cover, river water resources and water quality, and calibration studies. The AVIRISng data sets have been atmosphere-corrected through the standard NASA JPL data processing pipeline. Based on our preliminary evaluation of a few sets of AVIRISng data, we feel that the retrieved Level 2 surface reflectance data products have sufficiently good quality for research and applications over bright land surfaces. However, small residual artifacts are still present in data collected over darker water surfaces. For examples, the retrieved water leaving reflectances in the UV region over dark surfaces can be negative. In addition, spectral spikes are observed near atmospheric water vapor and oxygen band absorption regions as well as over regions containing extra-terrestrial solar lines. These spikes are most likely caused by errors in wavelength calibrations. The artifacts in the Level 2 surface reflectance data products can introduce errors in positive identification of subtle absorption features of various organic compounds in waters. We propose to apply practical techniques, including the method based on modeling white cloud spectral reflectance properties, to improve the absolute radiometric calibrations in the UV region. We also plan to match the atmospheric O2 bands, water vapor bands, and solar lines in AVIRISng-measured spectra with those from theoretical calculations in order to refine wavelength calibrations for each column of pixels in the direction perpendicular to the aircraft flight direction (the cross track direction). A small mis-alignment between the AVIRISng entrance slit and focal plane (a tilt) has introduced small column dependent wavelength shifts, and we hope to accurately characterize wavelengths for each column in the cross-track direction. After improvements in radiometric and spectral calibrations of AVIRISng data, better quality L2 surface reflectance data products, such as color dissolved organ matter, can be retrieved. We also propose to develop new techniques utilizing the information contained in contiguous spectra between about 400 and 860 nm for retrieving concentrations of suspended sediment, different types of chlorophylls, and other optically active constituents. We will make improved use of information contained near the 700 nm chlorophyll fluorescence peak for chlorophyll retrievals when the Chl concentration is 10 mg/m^3 or larger. We will use a narrow reflectance peak centered near 810 nm for the retrieval of suspended sediment concentration over very turbid waters with concentration of 30 g/m^3 or greater. This proposed research is in line with the research topics of 'river water resources and water quality', 'biological oceanography', and 'calibration studies', as listed in the NASA A.31 research announcement
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