Minimize Proba-V Cal/Val
Minimize Validation Activities

The radiometric and geometric accuracy of the instrument is routinely validated using a combination of vicarious calibration methods (e.g., Desert, Rayleigh, Deep Convective Clouds). A detailed description of some of these methods is available here

The results of the routine vicarious calibration processing are available on a quarterly basis in the "Image Quality Reports" generated by VITO, see the full list of reports here

The current results for geometric and radiometric accuracy verification are summarized here below.

  • Radiometric accuracy: The absolute and relative radiometric accuracy is periodically monitored using a combination of vicarious calibration approaches: i.e., Rayleigh, Desert and Deep Convective Clouds methods. Long-term radiometric stability is additionally verified using pseudo-invariant calibration sites (Libya-4 desert), which are acquired as part of the nominal planning, and special moon observations, which are monthly acquired with a special pitch manoeuver (360° rotation). The radiometric performances retrieved with these methods are excellent and very stable along the mission: absolute and relative radiometric accuracies are respectively better than 5% and 3%, radiometric stability is well within 3%. Cross-comparison with Landsat-8 show an agreement of better than 2% for all bands as summarized in Fig.1, see detailed results of this inter-comparison here.

Fig.1 - Overall average of the fraction calibration parameters (Proba-V/Landsat-OLI) derived by applying the same desert calibration method over Libya-4 site.

Fig.1 - Fraction of the averaged calibration parameters for Proba-V with respect to Landsat-8 OLI for the 4 Proba-V bands. The calibration parameters were derived by applying the same desert calibration method over Libya-4 site. (Image credits: VITO)

 

 

 

 

 

  • Geometric accuracy: The absolute and relative (inter-band) geo-location accuracy is daily monitored using ground control points, extracted from the Landsat GeoCover dataset. This monitoring allowed to detect an issue with the on-board handling of the star tracker attitude data during the first months of 2014, owing to this anomaly a significant degradation of the geometric accuracy was observed. After a long investigation, the root cause of the problem was found and the issue was solved on 10 March 2014 by applying an on-board patch. Since that date the geometric performances of Proba-V remain at an excellent level and very stable (see Fig.2), with an average absolute geo-location error of better than 50m and a relative error as low as 32 m for the RED-NIR bands. 

Fig.2 - Proba-V Average Location Error (ALE) in meters from Aug 2013 to Apr 2015. The ALE is determined using a set of GCP extracted from Landsat GeoCover database. The on-board star-tracker anomaly at the beginning of the mission is clearly visible, it was solved with an on-board patch during March 2014. Since then the ALE is stable around a mean value of 60m. (Image credits: VITO).

 

 

Fig. 3 - Animation showing the daily absolute geolocation error (m) in the across-track and along-track direction during the first months of the Proba-V mission. The impact of the star-tracker on-board anomaly is clearly observed in the first days of the animation and up to March 2014, when the upload of a SW patch allows to solve the attitude problem and significantly improve the geolocation accuracy. The different colours represent the four Proba-V bands, and the circles are respectively the goal requirements for absolute geolocation in the VNIR (300m) and in the VNIR+SWIR (450m). We can clearly see that after the correction of the on-board star-tracker anomaly both goal requirements are always met.