Galactic noise and passive microwave remote sensing from space at L-band

Abstract

The spectral window at L-band

The Salinity Retrieval Algorithms for the NASA Aquarius Version 5 and SMAP Version 3 Releases

“…Another large source of error that needs to be corrected in the salinity retrieval algorithm is the reflected radiation from the galaxy [20]. It can be large (5 Kelvin) and is difficult to deal with as it requires an accurate knowledge of the location and strengths of the galactic radiation, an analytic model for the wind induced roughness of the ocean surface and the antenna gain pattern.…”

“…The (relatively) strong reflected radiation emanating from the plane of the galaxy can appear in both the forward and the backward look but usually not at the same time. Radiation from directions other than the plane of the galaxy are generally quite small [20]. If all other signals that depend on look direction (Faraday rotation, wind direction, solar and lunar radiation) have been accurately removed [7], then taking the difference between fore and aft measured TA produces the reflected galactic radiation:…”

“…The galactic tables themselves, which were derived from radio astronomy measurements [20,21]. For example, there is a small polarized component and Cassiopeia A is very strong and variable.…”

“…Location and strength of the galactic sources at L-band are taken from the galactic map [20,21], which was derived from radio-astronomy observations. In actuality, bistatic scattering from a rough ocean will result in galactic radiation entering the mainlobe of the antenna from many different directions.…”

Aquarius and Remote Sensing of Sea Surface Salinity from Space

“…The total contribution can be more than 12 K in the direction of the plane of the galaxy even when smoothed by the aperture of large antennas like Aquarius (Le Vine and Abraham, 2006). Fortunately, modern surveys have been made by the radio astronomy community of these sources and a model for the L-band "sky" exists that can be used to characterize the contribution of these sources (Le Vine and Abraham, 2004;Wolleben et al, 2006). An open issue that will most likely not be resolved until after launch is the impact of surface roughness on this signal Reul et al, 2007].…”