USO Clock Period Measurements

One of the critical elements of the Radar Altimeter systems is the USO (Ultra Stable Oscillator) as it clocks the Altimetric Range Measurements. The variation in times of the USO clock period generates errors in the Range Measurements, recommended to be corrected by the end user.
Two sets of corrections are available:

• USO clock period measurements and correction before the USO Anomaly (before 1st February 2006)
• USO clock period measurements and correction after the USO Anomaly (after 1st February 2006)

The first set should be used for data processed with the Envisat Level 1B Instrument Processing Facility (IPF) versions up to V4.58,24th October 2005, which should be corrected for the USO clock period long term drift and bias.

The second set should be used for data processed with higher IPF versions, after the 1st February 2006. Data should be corrected for the USO clock period long term drift, bias and orbital variations due to the abnormal behavior of the USO Clock Period.

Data acquired from 24th October 2005 until 1st February 2006 should not be corrected given that the proper value of the USO clock period has been used within the L1b processing.

Click on the links above for complete descriptions of the measurements, corrections, and file-naming conventions.