Minimize Proba-V Cal/Val
Minimize Calibration Activities

Proba-V has no on-board calibration device, therefore the in-flight calibration is performed using Vicarious Calibration methods based on acquisition of specific target on-ground. Calibration measurement acquisition, processing and analysis is fully automatic and it is performed by the Cal/Val facility (OSCAR) developed by the Image Quality Center (IQC) at VITO. The usage of such vicarious calibration approaches allows to meet the goal requirements for the mission, i.e., 5% and 3% in absolute and relative radiometric accuracy, 300m and 100m in absolute and relative geometric accuracy.

Cal/Val acquisitions during Proba-V nominal operations are summarized here below, as described by the Cal/Val Plans for radiometry and geometry.

 

Daily Calibration acquisition

  • Acquisition over defined oceanic sites, to be used for Rayleigh Calibration
  • Acquisition over defined oceanic cloudy sites, to be used for Deep Convective Clouds Calibration
  • Acquisition over a number of oceanic sites, to be used for Sun-glint Calibration
  • Nominal acquisition over desert site (Libya-4) for radiometric absolute calibration and stability monitoring
  • Camera to camera bias adjustment using nominal acquisition
  • Geometric Calibration based on Ground Control Points (GCP) and nominal acquisition
  • Antarctica (only during December/January): acquisition in compressed mode (at least) 3 to 4 times a day; during one week daily for 2 orbits acquisition in uncompressed mode
  • Greenland (only during June/July): during one week daily acquisitions in uncompressed mode
Weekly Calibration acquisition
  • Dark current (oceans night) acquisition of at least 500 lines during night for each of the integration times over 1 site. At new moon these data should be acquired during the same night
Monthly Calibration acquisition
  • Moon observations at a phase angle of 7°, to be used for radiometric stability monitoring
6-Monthly Calibration
  • Linearity Check for each band for 5 targets
  • At least 45000 lines for each pixel of miscellaneous sites (April/October)
Ad-hoc Calibration/Validation
  • Cross-comparison with other optical sensors (e.g., Landsat) over Pseudo-Invariant Calibration Sites, such as Libya-4
  • Apex underflight cross-comparison
ProbaV_AutoE
IQC OSCAR tools for absolute, inter-band and multi-temporal calibration (image credit: VITO)