USO Clock Period Measurements prior to 01/02/206

This applies for data processed with the Envisat Level 1B Instrument Processing Facility (IPF) versions up to V4.58.

The Envisat RA-2 USO clock period measurement is evaluated by means of the ratio between the USO clock counter difference over a fixed time (one orbit), provided in the telemetry, and the corresponding UTC difference.

USO File Correction Description

One file per day is generated, sampled at 1Hz. The naming convention is as follows:

cycle_NN*/USO_clock_Delta_Range_yyyymmdd_YYYYMMDD.zip

Where:

yyyymmdd:      start date
YYYYMMDD:      stop date

* = cycle number

The format description corresponds to:

j_day: Julian day with respect to 1 January 1950.	

Range_correction: Correction (in mm) to be applied to the 
                  range in order to correct for the USO clock 
                  period variations. 
                  WARNING (to be subtracted from the range given 
                  in the products)

USO_clock_period: USO clock period (in ps)	

The format of the files is binary and it is coded as follows:

j_day, Range_correction, USO_clock_period, format=(3(f20.10, a2))

The user should be aware of the fact that, considering the units of measurements, for the Range_correction, the decimal figures are not really significant, while for the USO_clock_period only the first 6 decimal figures are significant.