These biases were estimated for each repeat cycle, but average values were
determined for each phase. The small variations from cycle to cycle probably do
not represent real variations but rather, uncertainty in the estimates. An
average for each phase was considered likely to be a more accurate
representation of the true bias for that interval of time. The following table
lists the average values estimated for the ERS-1 altimeter data for each phase.
The latest version of this table is maintained in the same directory as the
orbit files.

              Altimeter      Time Tag      EM Bias
 Phase        Bias (cm)      Bias (ms)    (% of SWH)
   A           -44.2           1.94          0.28
   B           -44.2           1.94          0.28
   C           -44.2           1.66          0.25
   D           -44.3           1.60          0.06
 E & F         -43.6           1.52          0.09
   G           -52.4           1.65          0.26

Notes:  

1)The altimeter range bias is relative to a reference sea surface defined by
T/P. The bias in the T/P altimeter is close to zero. A negative value indicates
that the ERS-1 altimeter is measuring short. The uncertainty is estimated to be
a few cm.

2) The time tag bias is in milliseconds. This value must be added to the
altimeter time tag to arrive at the correct time tag, which would be used to
call the orbit interpolator. The uncertainty is estimated to be approximately
0.2 ms.

3) The EM bias correction is estimated as a scale factor multiplied by the
significant wave height (SWH). A positive value indicates that the magnitude of
the EM bias correction must be increased, making the altimeter range shorter.
The uncertainty is estimated to be roughly 0.2%.