ICID 62 => SUN_VOLUME_SPECTRAL

Illumination:

  • Sun irradiance over the quartz volume reflection diffuser.

Purpose:

  • Spectral zoom-in sun irradiance measurements over the quartz volume reflection diffuser.
  • Provides spectral zoom-in sun irradiance level-1b data product for normalisation of Earth radiance spectra to obtain sun-normalised Earth radiances, or absolutely calibrated Earth reflectances.

Location:

  • Near the north pole, first light measurements, then dark measurements.

Usage:

  • Launch and Early Operations Phase (LEOP). Not used after 22 September 2004 (orbit 1007).

Description:

Sun over quartz volume reflection diffuser spectral zoom-in measurement. First, 77 light measurements are performed at changing elevation angles (roughly in the range +4.0 degrees to -4.0 degrees), then 77 dark measurements are performed. As a function of the day in the year (season) the azimuth angle on the diffuser changes. The individual sun irradiance measurements in the elevation angle range between -3.0 degrees and +3.0 degrees are averaged in the 0-1 data processor to obtain the level-1b irradiance data product. Averaging is performed to reduce the impact of spectral and spatial diffuser features and to improve the signal-to-noise. The dark (background) measurements of ICID 63 are eventually used to correct these light measurements in the 0-1 data processing.