Journal
REMOTE SENSING OF ENVIRONMENT
Volume 158, Issue -, Pages 207-219Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.rse.2014.11.014
Keywords
Imaging spectroscopy; Earth observation; APEX; Calibration; Processing; Validation; Earth science applications
Funding
- University of Zurich
- ESA PRODEX [16298/02/NL/US, 15449/01/NL/Sfe]
- Swiss National Science Foundation (SNSF)
- Belgian Science Policy Office (BELSPO)
- Swiss University Conference (SUK, KIP-SEON)
- University of Zurich Research Priority Program on 'Global Change and Biodiversity' (URPP GCB)
- Swiss Space Office (SSO)
- European Metrology Research Programme (EMRP) - EMRP within EURAMET
- European Metrology Research Programme (EMRP) - European Union
- ESA
- German Aerospace Center (DLR)
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We present the Airborne Prism Experiment (APEX), its calibration and subsequent radiometric measurements as well as Earth science applications derived from this data. APEX is a dispersive pushbroom imaging spectrometer covering the solar reflected wavelength range between 372 and 2540 nm with nominal 312 (max. 532) spectral bands. APEX is calibrated using a combination of laboratory, in-flight and vicarious calibration approaches. These are complemented by using a forward and inverse radiative transfer modeling approach, suitable to further validate APEX data. We establish traceability of APEX radiances to a primary calibration standard, including uncertainty analysis. We also discuss the instrument simulation process ranging from initial specifications to performance validation. In a second part, we present Earth science applications using APEX. They include geometric and atmospheric compensated as well as reflectance anisotropy minimized Level 2 data. Further, we discuss retrieval of aerosol optical depth as well as vertical column density of NOx, a radiance data-based coupled canopy atmosphere model, and finally measuring sun-induced chlorophyll fluorescence (Fs) and infer plant pigment content. The results report on all APEX specifications including validation. APEX radiances are traceable to a primary standard with <4% uncertainty and with an average SNR of >625 for all spectral bands. Radiance based vicarious calibration is traceable to a secondary standard with <= 65% uncertainty. Except for inferring plant pigment content, all applications are validated using in-situ measurement approaches and modeling. Even relatively broad APEX bands (FWHM of 6 nm at 760 nm) can assess Fs with modeling agreements as high as R-2 = 0.87 (relative RMSE = 27.76%). We conclude on the use of high resolution imaging spectrometers and suggest further development of imaging spectrometers supporting science grade spectroscopy measurements. (C) 2014 The Authors. Published by Elsevier Inc.
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