SMOS L2 OS ATBD - ARGANS

77
ICM-CSIC
LOCEAN/SA/CETP
IFREMER
SMOS L2 OS
Algorithm Theoretical
Baseline Document
Doc: SO-TN-ARG-GS-0007
Issue: 3 Rev: 9
Date: 25 January 2013
Page: 77
In order to examine the stability of the roughness residuals over time we have evaluated the
residuals on two independence set of SMOS data: ‘old’ passes from March through May
2010 and ‘new’ passes from August through October 2010. The residuals at 61 deg incidence
angle are shown below and reveal less than 1 K difference between the two sets of data at 25
m/s wind speed. This, along with the comparison between NCEP and ECMWF winds,
provides an indication of the uncertainty of the roughness residuals.
To assess the impact of using the empirically determined roughness residuals instead of the
theoretical residuals, we collected a set of several hundred Pacific Ocean passes and
evaluated the bias between the SMOS brightness temperatures and the complete theoretical
and empirical models averaged over the alias-free field of view. We collected these biases in
terms of (Tx+Ty)/2 and plotted them as a function of time and boresight latitude, and the
results for descending passes from March 1 to November 1 2010 are shown below for the
theoretical SSA/SPM model. Aside from the large negative bias in June and July, we can see
areas of large negative biases associated with storms in the southern hemisphere. These
biases correspond to roughness emission overestimation by the sum of the SSA/SPM and
foam models.