Image of the month News
12.04.2010 08:41 Age: 14 yrs
[Jason-1] Large off-nadir angles since March 2010
Category: Operational news
Since mid-March, a degradation of the on-orbit performance of the star trackers and gyro wheels on Jason-1 has caused large off-nadir angles of the platform.
The most immediate impact has been on the Jason-1 Near-Real-Time OSDR products, because the altimeter retracking algorithm used for the OSDR products requires off-nadir angles less than 0.3 degrees. For example, since April 1 more than 15% of the SWH values reported on the OSDR products have been set to the default value.
There is a lower impact on the Jason-1 I/GDR products because the MLE4 ground retracking algorithm used for these products allows off-nadir angles up to 0.7 degrees.
However, during the past 3 days, off-nadir angles have been larger than 0.7 degrees, and in some cases has been large enough that altimeter has lost track. This loss of track has resulted with data gaps in the observation record. The Jason-1 project is investigating options to improve the situation. We apologize for the inconvenience.
The most immediate impact has been on the Jason-1 Near-Real-Time OSDR products, because the altimeter retracking algorithm used for the OSDR products requires off-nadir angles less than 0.3 degrees. For example, since April 1 more than 15% of the SWH values reported on the OSDR products have been set to the default value.
There is a lower impact on the Jason-1 I/GDR products because the MLE4 ground retracking algorithm used for these products allows off-nadir angles up to 0.7 degrees.
However, during the past 3 days, off-nadir angles have been larger than 0.7 degrees, and in some cases has been large enough that altimeter has lost track. This loss of track has resulted with data gaps in the observation record. The Jason-1 project is investigating options to improve the situation. We apologize for the inconvenience.
