Measuring Snow Depth. Assignment 4. Due February 8

Discussion: Review the information from the Snow Booklet on measuring snow and precipitation. Review also the information on the Judd Communications depth sensor.

An ultrasonic pulse travels from the transducer (sensor) to a surface and back again. The length of time that the pulse takes can be converted to a distance, when the temperature of the air is known.

Indoor evaluation of sensor beam

• Evaluation of sensor beam width. Major obstacle. The beam width of the sensor is reported to be 22 degress. Determine for the placement of the sensor in the lab, the locations that should be monitored by the sensor. Stand the metal bar at various locations within this area and determine the beam width over which a major obstacle is detected. Does the sensor take the average of the distance to the major obstacle and the rest of the floor?

• Evaluation of sensor beam width. minor obstacle. Lay the metal pipe on the floor in the marked area. At what angular distance does the sensor detect the pipe? At what angular distance does the sensor measure the actual width of the pipe?

• Impact of moisture on temperature sensor. Lightlyspray some water on the thermistor so that the temperature will be the wet bulb temperature. What impact does the change in temperature measured by the sensor have on the distance to the floor? Explain what is happening.

Outdoor evaluation of sensor

• Irregular surface. Carefully take the weather station outside. Place the sensor on a flat surface where there is some snow. Shove the snow around to make different types of spatial distributions sampled by the sensor. How does the sensor respond to the different distributions?

Discuss other sources of error in measuring snow depth.

Snow properties

• Water equivalent and density of snow pack.
  • Use the coring tube to extract a representative snow sample in a location where you have made a measurement of snow depth. Put the sample in the jar.
  • Back in the lab, melt the sample and measure the amount of water equivalent (in ml equivalent to cm^3).
  • Using the snow depth and cross-sectional area of the tube, estimate the density of snow (i.e., 10% density would be .1 inches of water to 1 inch of snow depth).
  • Discuss many of the sampling problems and other errors that could be affecting your estimate.

• Crystal structure
  • Several students took observations as the snow was falling. Record your observations in terms of crystal structure according to the classification provided on the accompan ying sheet and make those available to those who were not present. See also Snow crystal primer
  • Record your observations on crystal structure today.
  • How has the snow changed during the 1 day period? Relate the changes in crystal structure to the temperature and cloud cover observed during the 1 day period.