Launched with an aim to map global soil moisture and detect whether soils are frozen or thawed, NASA's new Soil Moisture Active Passive (SMAP) observatory has successfully generated its first global maps.The mission will help scientists understand the links among Earth's water, energy and carbon cycles - a key step to begin routine science operations next month.It will also help reduce uncertainties in predicting weather and climate and enhance our ability to monitor and predict natural hazards such as floods and droughts, the US space agency said in a statement.In late March, mission controllers at NASA's Jet Propulsion Laboratory in Pasadena, California, successfully spun SMAP's 20-foot-wide antenna up to its full speed of 14.6 revolutions per minute in a two-step process.
SMAP's spinning antenna makes cone-shaped scans across Earth's surface, measuring a 1,000-km swath of the ground as it flies above Earth from pole to pole at an altitude of 685 km.The wide swath width and polar orbit allow SMAP to map the entire globe with high-resolution radar data every two to three days.The radar data acquired from the test have been processed to generate data products with a spatial resolution of about 30 km.In the global map, the Amazon and Congo rainforests produced strong emissions, depicted in red shades, due to their large volumes of biomass.Brightness temperatures in the Sahara Desert reach about 80 degrees Fahrenheit (about 300 Kelvin) due to its low moisture content.
The impact of soil moisture is evident over a large region south of the Great Lakes, where an increase in soil moisture due to precipitation in March resulted in relatively cool brightness temperatures of about minus 100 Fahrenheit (about 200 Kelvin).Similar impacts of rain on soil moistures and brightness temperatures are seen in Namibia and Botswana, Africa, where there was significant rainfall in late March.
The SMAP mission is required to produce high-resolution maps of global soil moisture and detect whether soils are frozen or thawed.Scientists will combine measurements from SMAP's radar and radiometer sensors to capitalise on the strengths of each and work around their weaknesses.The radar alone can produce a soil moisture measurement with a spatial resolution of about three km, but the measurement itself is less accurate than the one made by the radiometer.The radiometer alone achieves a highly accurate observation of soil moisture but with a much poorer spatial resolution of about 40 km.By combining these separate measurements through advanced data processing, SMAP will provide the user community with a combined soil moisture measurement that has high accuracy and a resolution of nine km.