Operational assimilation of ASCAT surface soil wetness at the Met Office

Abstract

Abstract. Currently, no extensive, near real time, global soil moisture observation network exists. Therefore, the Met Office global soil moisture analysis scheme has instead used observations of screen temperature and humidity. A number of new space-borne remote sensing systems, operating at microwave frequencies, have been developed that provide a more direct retrieval of surface soil moisture. These systems are attractive since they provide global data coverage and the horizontal resolution is similar to weather forecasting models. Several studies show that measurements of normalised backscatter (surface soil wetness) from the Advanced Scatterometer (ASCAT) on the meteorological operational (MetOp) satellite contain good quality information about surface soil moisture. This study describes methods to convert ASCAT surface soil wetness measurements to volumetric surface soil moisture together with bias correction and quality control. A computationally efficient nudging scheme is used to assimilate the ASCAT volumetric surface soil moisture data into the Met Office global soil moisture analysis. This ASCAT nudging scheme works alongside a soil moisture nudging scheme that uses observations of screen temperature and humidity. Trials, using the Met Office global Unified Model, of the ASCAT nudging scheme show a positive impact on forecasts of screen temperature and humidity for the tropics, North America and Australia. A comparison with in-situ soil moisture measurements from the US also indicates that assimilation of ASCAT surface soil wetness improves the soil moisture analysis. Assimilation of ASCAT surface soil wetness measurements became operational during July 2010.

JASMIN: A prototype high resolution soil moisture analysis system for Australia

“…New flexible land data assimilation systems have been developed that can assimilate a wide variety of measurements such as 2 m temperature and humidity, satellite derived surface soil wetness, satellite derived land surface temperature and vegetation properties such as LAI (e.g. Dharssi et al 2012Dharssi et al , 2011. The data assimilation can also propagate the surface information into the deeper soil layers.…”

“…ASCAT also shows high skill at all sites except Tumbarumba which is a wet sclerophyll eucalyptus forest site and Tullochgorum which is surrounded by high terrain. ASCAT has already been shown to perform less well in regions with dense vegetation or complex terrain (Dharssi et al 2011). CosmOz appears to have only moderate skill at Tumbarumba and this may be because of the high vegetation density.…”

“…Remotely sensed satellite measurements are used to derive the soil albedo (Houldcroft et al 2009) , land-cover types (Loveland et al 2000), LAI (Samanta et al 2008) and forest canopy height (Simard et al 2011). The ancillary data can have a significant impact on model results (Dharssi et al 2009.…”

Downscaling of seasonal soil moisture forecasts using satellite data

“…Soil moisture has a significant impact on near-surface parameters like temperature and humidity, low clouds and precipitation by influencing the exchange of heat and water between the soil and the lower atmosphere (Ferranti and Viterbo, 2006;Dharssi et al, 2011). Evapotranspiration, infiltration and runoff depend on soil wetness, as does the sensible heat flux from the surface and the heat stored in soils.…”

Spatial horizontal correlation characteristics in the land data assimilation of soil moisture

“…Li et al (2010), , Reichle et al (2007), Tian et al (2010) and Yang et al (2009) proved that the assimilation of real passive microwave remotely sensed surface soil moisture or brightness temperature could improve the model estimation of soil moisture. The soil moisture products of scatterometer were also used in data assimilation (Dharssi et al, 2011;Mahfouf, 2010;Brocca et al, 2010b). Pan and Wood (2010) analyzed the impact of satellite spatial availability on the soil moisture assimilation in a synthetic experiment.…”