Study of the spectral gradient of frozen soil

Spectral gradient is one of the indicators of soil freeze and thaw. A negative spectral gradient was a sign of frozen soil. A truck-mounted microwave radiometer observed the frozen ground in two experiments. However, the measured spectral gradient was positive when the surface is frozen. From experiment measured and model simulated result, the relationship between the amount of unfrozen water of frozen soil and SG was found. It indicates that the amount of unfrozen water is a very important factor that determines the microwave radiation of frozen soil.