A soil moisture and temperature network for SMOS validation in Western Denmark

摘要

The Soil Moisture and Ocean Salinity Mission (SMOS) acquires surface soilmoisture data of global coverage every three days. Product validation for arange of climate and environmental conditions across continents is a crucialstep. For this purpose, a soil moisture and soil temperature sensor networkwas established in the Skjern River Catchment, Denmark. The objectives ofthis article are to describe a method to implement a network suited for SMOSvalidation, and to present sample data collected by the network to verify theapproach. The design phase included (1) selection of a single SMOS pixel(44 × 44 km), which is representative of the land surfaceconditions of the catchment and with minimal impact from open water(2) arrangement of three network clusters along the precipitation gradient,and (3) distribution of the stations according to respective fractions ofclasses representing the prevailing environmental conditions. Overall,measured moisture and temperature patterns could be related to the respectiveland cover and soil conditions. Texture-dependency of the 0–5 cm soilmoisture measurements was demonstrated. Regional differences in 0–5 cm soilmoisture, temperature and precipitation between the north-east and south-westwere found to be small. A first comparison between the 0–5 cm networkaverages and the SMOS soil moisture (level 2) product is in range withworldwide validation results, showing comparable trends for SMOS retrievedsoil moisture (R2 of 0.49) as well as initial soil moisture andtemperature from ECMWF used in the retrieval algorithm (R2 of 0.67 and0.97, respectively). While retrieved/initial SMOS soil moisture indicatesignificant under-/overestimation of the network data (biases of?0.092/0.057 m3 m?3), the initial temperature is in goodagreement (bias of ?0.2 °C). Based on these findings, the networkperforms according to expectations and proves to be well-suited for itspurpose. The discrepancies between network and SMOS soil moisture will besubject of subsequent studies.