CREST-Snow Analysis and Field Experiment


Microwave Radiometers:
The set of instrumentation installed includes two dual-polarization microwave radiometers manufactured by Radiometrics Corp and operating at 10.65, 19, 37 and 89 GHz. . All instruments are mounted on top of a trailer at about 4m height and are pointed at the surface at an incidence angle of 55 degrees. The value of the observation angle was selected to match the observation geometry of Special Sensor Microwave Imager (SSMI) onboard DMSP satellites and Advanced Microwave Scanning Radiometer AMSR-E  onboard Aqua satellite Measurements of the microwave brightness temperature at two frequencies are taken routinely at one minute interval. To ensure high accuracy of the measurements microwave radiometers were calibrated twice, in the beginning and in the middle of the winter season.

Gamma Radiation Sensor
The Gamma radiation sensor (CS725) obtains the measurements by passively monitoring the attenuation of naturally existing electromagnetic radiation, due to the presence of potassium and thallium. As snow accumulates on top of the ground, the CS725 measures a decrease in the normal background radiation levels. The higher the water content, the higher the attenuation of the radiation. The CS725 has several characteristics that make it an excellent sensor for SWE measurement applications.
Cimel sunphotometer
The Cimel sunphotometer (CSPHOT) is a multi-channel, automatic sun-and-sky scanning radiometer that measures the direct solar irradiance and sky radiance at the Earth's surface. Measurements are taken at pre-determined discrete wavelengths in the visible and near-IR parts of the spectrum to determine atmospheric transmission and scattering properties. 

Snow Temperature Profiler
Observations of the temperature vertical distribution in the snow pack were measured with a specially developed temperature profiler. The instrument was built with 16 Watlow Rigid Sheath Thermocouples placed  at 5 to 10 cm  interval.


Snow Wetness Sensor
Observations of the snow permittivity vertical distribution in the snow pack were measured with a specially developed wetness profiler. This instrument was built with 14 CS 650 soil reflectometers at 10 to 15 cm intervals.

Solar Radiation Sensor
The CMP3 is an ISO-second-class pyranometer that monitors solar radiation for the full solar spectrum range. It connected directly to a Campbell Scientific datalogger.
Infrared Temperature Sensor (for Skin Temperature)
Apogee Instruments Infrared Radiometers (IRRs) measure surface temperature by converting thermal energy radiated from any surface in its field-of-view (FOV) to an electrical signal with a response time less than 1 second. Each IRR carries an impressive uncertainty of 0.2°C at 95% confidence to ensure accurate measurements.

Ultrasonic Snow Depth Sensor
The sensor works by measuring the time required for an ultrasonic pulse to travel to and from a target surface. An integrated temperature probe with solar radiation shield provides an air temperature measurement for properly compensating the distance measured.


Snow Pillow (for Snow Water Equivalent Measurement)
The snow pillow measures the water content of the snow layer based on hydrostatic pressure created by overlying snow. In simple words the weight of the water in the snow forces the fluid to the pressure transducer which converts the data to a signal that is directly transmitted to a Campbell Scientific data logger.


Stand Pipe Gauge (Snowfall and Rainfall rate measurement)  
The gauge consists of a storage bin, which is weighed to record changes in pressure, that is later converted in to the amount of precipitation. The advantages of this type of gauge over tipping buckets are that it does not underestimate intense rain, and it can measure other forms of precipitation, including rain, hail and snow.