Investigating the Temporal Variability in Salinity from Ascending and Descending Passes in SMOS and Aquarius
[16-Apr-2013] Banks, C., Gommenginger, C., Srokosz, M., and Snaith, H.
Presented at the 2013 SMOS-Aquarius Science Workshop
The launch of the SMOS and Aquarius satellites marked a new era in satellite oceanography allowing routine monitoring of the salinity of the world's oceans on synoptic scales. However, there are significant issues affecting the performance of SMOS related to the satellite direction (ascending/descending passes) although the magnitude has decreased with revised versions of the processor. On-going work has shown that Aquarius also has a bias between SSS from ascending passes and SSS from descending passes. The ascending/descending bias in SMOS SSS is significant and is likely, in part, linked to changes in galactic glint and sun contamination through the year. The ascending/descending bias for Aquarius is less pronounced but is still significant.
SMOS has a sun-synchronous orbit such that at ~6 a.m. (local time) SMOS is ascending (satellite moving from south to north) and at ~6 p.m. is descending (satellite moving north to south). Similarly, Aquarius is in a sun-synchronous orbit but the direction of passes is 12-hours out of phase so that Aquarius is ascending at ~6 p.m. and descending at ~6 a.m. This paper reviews work-to-date at the UK National Oceanography Centre on a study concerned with looking at differences amongst SSS derived from SMOS and Aquarius from ascending and descending passes. The aim is to take advantage of data from both satellites and utilise the phase difference to investigate whether time of day is a factor (e.g. biases due to diurnal warming effects or the tendency for heavy precipitation to occur mid-afternoon in tropical regions).
The study region is the global oceans between 60°S and 60°N and the data are from 1 September 2011 to 31 October 2012 for Aquarius (processor V1.3) and 1 September 2010 to 31 October 2012 for SMOS (processor V5_50). For SMOS and Aquarius separately, the mean, daily SSS from all descending passes is subtracted from the mean daily SSS from all ascending passes (SSSA-D). Both satellites show temporal variability in SSSA-D but the variations are not in phase. The study considers results globally as well as smaller regions and over latitudinal ranges.