A wireless sensor that can measure the local density, wetness, temperature and snow grain size of a snow pack will be designed, fabricated and validated in this effort. By minimizing the cost of replication of this instrument, sensor webs can be deployed that will characterize the considerable spatial variability of snow packs. By employing low power wireless technology, these sensors can monitor this spatial variability over time with minimal disturbance of the snow pack. Snow varies considerably vertically, due to variable accumulation from storms over the course of a winter season. Snow varies temporally, in response to forcings from atmospheric temperatures, insolation, and ground freeze-thaw state. Snow also varies horizontally, due to topography, vegetation variations, and from drifting. These variations of snow pack parameters are coupled. For example, snow grain size and snow pack density are a function of the temperature and liquid water content history of the snow pack. The fact that liquid water and water vapor can migrate in the snow pack means that single point measurements, either in space or in time, are insufficient to capture the full evolution of the snow pack. This instrument concept is a critical calibration/validation technology for the SCLP mission, since SCLP relies upon microwave radar and radiometry to extract macroscopic snow pack properties, such as SWE, but the microscopic properties that this sensor detects, especially the liquid water content, dramatically affects the microwave signature of snow packs. Thus, the extraction of temporally and spatially variable microscopic properties of a snow pack will permit the comparison of the SCLP (and precursor missions) observables to snow pack signature models with much more constrained model inputs than is currently possible. This is an enabling technology for comparing the information content of the remote sensing observables to the ground truth, by providing a sample size of necessary ground truth that is not currently available. The sensor will use a quarter wave open resonator operating around 900MHz to determine the snow density and liquid water content. An optical link spanning the length of the sensor will be used to quantify the snow grain size. The measurement set is completed with an electronic thermometer. The wireless design not only provides the greatest flexibility in deployment, but eliminates wires which are a path for anomalous heat and moisture transport to the sensor location. The communications link will employ UHF to insure maximum signal transmission even in a wet snow pack. This wireless sensor, and its base station that will be deployed above the snow pack, will be designed by experienced engineers in the University of Michigan's Space Physics Research Lab. An initial production run of sensor units will employ commercial pick-and-place vendor to demonstrate the ability to rapidly and economically produce many sensor units for a field campaign. Calibration of the moisture, density, temperature and grain size measurements will be performed on each sensor unit to demonstrate manufacturing repeatability. The project will conclude with a field deployment, coupled with periodic traditional, labor-intensive stratigraphic measurements of the snow pack parameters to validate the instruments' performance. This field deployment will take place at the University of Michigan's Biological Station in Pellston, MI, a site that sports a wide variety of terrain types in one of the snowiest locations in the region.