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Proceedings Paper

Spectroradiometric calibration and validation of space instruments used to derive long-term changes in stratospheric ozone using the solar backscattered ultraviolet radiation technique
Author(s): Donald F. Heath; Zongying Wei; Ernest Hilsenrath; William K. Fowler; V. Wayne Nelson; Roel Hoekstra; Carina Olij; Scott J. Janz
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Paper Abstract

Beginning in the mid 1960's large aperture scanning radiometers have been used in space to determine spectroradiometric properties of earth scenes in the red and near infrared regions. Panel diffusers as calibration sources for these radiometers were abandoned in favor of internally illuminated integrating spheres because of problems of illuminating the panel diffuser uniformly.1 Since 1970 spectroradiometric instruments used in space for remote sensing of the atmosphere in the ultraviolet for the determination of stratospheric ozone and total column amounts have used spectral radiance calibrations derived from calibrated panel diffusers illuminated by NIST standards of spectral irradiance. An advantage of the panel diffuser technique is simplicity of the experimental set up. Stratospheric ozone profiles and total column amounts are derived from ratios of atmospheric radiances to corresponding solar irradiances incident at the top of the atmosphere in the wavelength region of 250 - 340 nm. An inherent problem associated with measurements for the remote sensing of stratospheric ozone which is not shared with remote sensing measurements of earth scenes at longer wavelengths of the solar scattering and reflective region is the extremely large dynamic range of atmospheric radiances and the steep gradients of radiance with wavelength. For a typical wavelength scan the spectral radiance changes by about lO and the average signal level of a spectral scan can shift by another factor of 25 or more due to solar zenith angle changes between the subsolar point and the solar zenith angle limit of useful scan information which is within a couple of degrees of the terminator. The derivation of spectral radiance calibrations using either the sphere or panel diffuser techniques for ultraviolet remote sensing instruments are single point calibrations at each wavelength. A subsequent linearity calibration of the detector and electronics is made in non dispersed or white light over the entire dynamic range of the instrument of more than six decades. Consequently the derived radiometric calibration constants consist of a radiometric sensitivity term and a signal dependent linearity correction. An initial comparison of spectral radiance calibrations of SBUV-2 instruments using spherical integrator and panel diffuser techniques has been given by Heath et al.2. Subsequent work by Heath et al. describes the results from comparisons of four spectral radiance calibrations derived using panel diffuser techniques with five spectral radiance calibrations derived using spherical integrator techniques for three different SBUV-2 instruments. The comparability of the sphere and panel diffuser spectral radiance calibration techniques is assesed by comparing derived average BRDF values of panel diffusers based upon the sphere technique with laboratory measurements of BRDF of the panel diffusers. The sphere radiances determined relative to NIST standards of spectral irradiance are compared with measurements of sphere radiance relative to a NIST high temperature blackbody source. This work describes the evaluation of the consistency of spectral radiance calibration scales established using panel diffuser and internally illuminated spherical integrator techniques for the SSBUV and SBUV-2 Flight Model 5 instruments using zenith sky radiance measurements as a function of solar zenith angle (UMKEHR) which coincident in space and time. Also described are the spectral radiance calibrations of the Global Ozone Monitoring Experiment (GOME) with the NASA sphere which has been used to intercalibrate SBUV-2 and SSBUV instruments. These spectral radiance calibration constants are compared with those derived using a Spectralon panel diffuser whose BRDF was measured at NASA Goddard Space Flight Center by J. Butler.

Paper Details

Date Published: 21 December 1994
PDF: 14 pages
Proc. SPIE 2318, Recent Advances in Remote Sensing and Hyperspectral Remote Sensing, (21 December 1994); doi: 10.1117/12.197235
Show Author Affiliations
Donald F. Heath, Research Support Instruments Inc. (United States)
Zongying Wei, Research Support Instruments Inc. (United States)
Ernest Hilsenrath, NASA Goddard Space Flight Ctr. (United States)
William K. Fowler, Ball Electro-Optics and Cryogenics Div. (United States)
V. Wayne Nelson, Ball Electro-Optics and Cryogenics Div. (United States)
Roel Hoekstra, TNO Institute of Applied Physics (Netherlands)
Carina Olij, TNO Institute of Applied Physics (Netherlands)
Scott J. Janz, IDEA Inc. (United States)

Published in SPIE Proceedings Vol. 2318:
Recent Advances in Remote Sensing and Hyperspectral Remote Sensing
Pat S. Chavez Jr.; Carlo M. Marino; Robert A. Schowengerdt, Editor(s)

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