The effect of soil temperature on FDR soil moisture sensor near freezing point was analyzed under frozen and unfrozen
conditions based on datum including frozen soil, soil temperature and soil moisture from automatic FDR soil moisture
monitor at Anyang and Sanmenxia between 1st Dec. 2010 and 20th Feb. 2011. Results revealed that: The cycle of soil
temperature caused corresponding periodical variation of volume water content monitored by FDR sensor, and the
amplitude was larger in frozen days than that in unfrozen days. Between 0°C~10°C, soil temperature affect FDR sensor
results linearly, temperature correction coefficient of GStar-1 sensor is 0.16% (v/v) every degree, similar with coefficient
of PR2 from Delta-T. Temperature affects FDR sensor results exponentially below 0°C. FDR sensor can be used in
automatic frozen soil observation after the standard of unfrozen water content was defined in frozen soil.