Geolocation anomaly for 19 – 21 September 2018
For the period 19 – 21 September 2018, unusually high Absolute Location Errors were observed. We are currently investigating the root cause of this unexpected behavior. For the time being, all Level 2A segment and S1 data products within the above mentioned time period have been taken offline. The multi-day syntheses for 11 – 20 and 21 – 30 September (S10 products), and for 16 – 20 and 21 – 26 (S5 products) are still available, but do not contain segment data for 19 – 21 September in the calculated composites.
Once the root cause is found, the Level 2A segments and S1 synthesis products will become online again, while the S5 and S10 data products will be regenerated.
We apologize for any inconvenience this issue may cause and do our very best to have the data products for 19 – 21 September online again as soon as possible.
Degraded geometric performance
PROBA-V is a very stable platform in terms of geometric performance. It exceeds the mandatory absolute, Inter-bands and multitemporal accuracy by far. However, some occurrences are recorded that the satellite uses the Two Line Element (TLE) in case of a GPS failure leading to degradation of the geometric performance.
Below is a list of occurrences when the platform used the TLE and degraded performance might be expected:
Cloud Detection Issue in PROBA-V Collection 1 data
The modified PROBA-V cloud detection algorithm, which is used in the Collection 1 data, uses monthly land cover information, based on ESA Land Cover CCI data. Each pixel is assigned one of the following classes: ‘land’, ‘water’, ‘snow/ice’, ‘shadow’, ‘cloud’, and ‘unknown’. During the final Collection 1 validation we discovered that during the northern hemisphere winter season the amount of ‘unknown’ land cover assignments is unusually high, which eventually results in a substantial amount of clouds that are labelled ‘clear’.
This cloud detection issue impacts both the segment data (Level 2A), as well as the synthesis files at all product resolutions and is most prominent during the northern hemisphere winter season. The underdetection of clouds occurs primarily along a latitudinal band that shifts southward and reaches ~50oN as southernmost position.
We are currently investigating the cause and correction of this issue, further details will be communicated here once available.