How do satellites measure soil moisture?
Satellites measure how different frequencies of energy are reflected from the surface of the earth. Differences in reflected energy from the Earths surface can be related to soil moisture. Four main factors that influence the soil reflectance are mineral composition, soil moisture, organic matter and soil texture. Satellites measure the radiation or microwave energy at the surface of the earth in units of brightness, temperature and power. Satellite-measured soil moisture reflects an average soil moisture value for the top 5 to 10 cm only. An important part of interpreting soil moisture measurements from satellites is ground-truthing or comparing satellite determined soil moisture to measurements collected by hand in the field, which is why collecting soil moisture samples for the GLOBE program is a very valuable scientific effort.
