Lesson Plan
Title: Comparisons of NEXRAD radar and precipitation gauge values

The educational goal of this project is to engage undergraduate students in an inexpensive complex field research project in which they learn multiple research methods.
Students will be able to:
• choose locations where rain gauges should be sited through map discussion and considerations of land use factors
place rain gauges on site
• collect data after each precipitation event
• access Internet radar data
• input data into a spreadsheet
• analyze data statistically using basic spreadsheet calculations
• use geographic information systems (ArcView or ArcGIS) to produce overlays of spreadsheet and mapped data
• present results of study in class, on campus during speaker series, or at a local conference

• 2 x 4 boards, cut into ~5 feet long sections &1 for each rain gauge
• Simple plastic rain gauges, including bracket for mounting and screws (cost in early 2002 = $5.40 each). Check out www.nascofa.com.
• Drill
• Mallet
• Small scrap piece of durable wood, for use with mallet when pounding post into ground
• Measuring tape
• Labels for each board, including the name of a contact person, your school s name, phone number, and a warning sign requesting that passers-by not mishandle the equipment
• Data sheets (see example below)
• Use of vehicle unless rain gauges are within walking distance
• Global Positioning System (GPS) unit
• Current radar data off web (use www.weathertap.com or other site)
• Journal articles explaining radar technology (Serafin and Wilson, 2000; Fields, 1997 and other articles in bibliography below)
• Computer with Microsoft Excel, Word, PowerPoint, and ArcView or ArcGIS software
• Digital Camera with downloading software

Preliminary Discussion with Students
Before gathering materials and completing this field exercise, it is important to discuss with your students:
1. Reasons why there might be local precipitation variability,
2. The general climate of your region and the types of storm systems that generally move through your area,
3. How radar works and where the closest NEXRAD sites are located,
4. The importance of proper data collection techniques,
5. Inherent problems associated with data collection,
6. Use of a GPS unit, digital camera, and GIS,
7. The importance of ground truthing and why it is important to ensure that radar values are comparable to observed values at the ground surface,
8. The importance of precipitation receipt within the local watershed to the hydrology of the region.
After initiating these preliminary discussions, students will have the necessary background to embark upon the field project.Be sure to designate a specific timeframe for the research project.

Activity 1: Constructing and Siting the Precipitation Gauges
Have students choose a number of sites around school, and within a local watershed, to ensure proper representation across local land use types.Attempt to choose sites that are out of view.Also, site gauges away from structures or vegetation that could affect site-specific precipitation.Obtain permission to place rain gauges on public/private property.
Attach rain gauges to ~5 foot long, 2 x 4 boards (posts) using a drill and the screws that accompany the rain gauges.Pound posts into ground such that the top of all rain gauges is located at a standard height above the ground (we chose 120 cm).Attach the label including your contact information so anyone encountering the gauges understands that it is part of a school project, and that they should not tamper with the gauge.

Activity 2: Use of GPS, Digital Camera, and GIS
Using a Global Positioning System (GPS) unit, have students record the latitude, longitude coordinates at each rain gauge (see instructions in GPS manual).With the digital camera, take pictures of each rain gauge including a view of the surrounding vegetation or land use.Download the GPS coordinates and camera images to your computer in the classroom.Ask students to access a land use map of your local area and watershed (In Pennsylvania, available at http://www.depweb.state.pa.us/dep/cwp/view.asp?a=3&q=461149&depNav=|.) Map the array of rain gauges using GIS software like ArcView or ArcGIS.
Activity 3: Accessing NEXRAD Storm Total Precipitation Estimates
NEXRAD storm total precipitation estimates can be downloaded from the Internet (www.weathertap.com or other sites) for each event for which radar data are available.A small grant from Shippensburg University supported a one-year subscription to the Internet service which cost $63 per year in 2002 (free radar data are also available from a number of sites).It is important to copy the final storm total precipitation radar map after the conclusion of each storm event and before the next event begins.The radar data accessed through www.weathertap.com are in map form with a pixel resolution of approximately 2 km x 2 km and are saved as a digital graphic which helps with overlay later in the GIS.Also, each pixel is shaded with the radar data displayed according to the following ranges of storm total precipitation:
0.00 - 0.30 in (0 - 7.6 mm)1.01 –- 1.50 in(25.5 - 38.1 mm)
0.31 –- 0.60 in(7.7 - 15.2 mm) 1.51 - 2.00 in(38.2 - 50.8 mm)
0.61 - 1.00 in(15.3 - 25.4 mm) 2.01 - 2.50 in(50.9 - 63.5 mm)
This range is important for the students to understand when making comparisons later.

Activity 4: Precipitation Data Collection
As soon as possible after each rain event ends, have students travel to each field site to measure precipitation and completely empty each gauge.Return to the classroom and copy data manually from the data sheet into a spreadsheet (Excel is recommended.).Continue this procedure after each precipitation event for the duration of your designated field project.
Activity 5: Overlaying the Information
The NEXRAD storm total precipitation estimate for each site can be determined by digitally overlaying the map of rain gauge locations onto the map of radar precipitation values for each storm event using ArcView GIS.Due to differences in map projection, the overlay procedure requires either the Image Analyst ArcView extension (software sold separately) or the Image Warp extension (available for free download).It is necessary to zoom in so that each pixel of the radar-derived precipitation map can be identified and the precipitation range determined.Make comparisons between NEXRAD data and rain gauge totals for each storm event, computing whether NEXRAD over or underestimates the actual measured field values.For all cases in which the measured rain gauge values are outside the NEXRAD-estimated precipitation range, departures should be calculated as the difference between the rain gauge value and the closest end of the NEXRAD-estimated precipitation range.The departures will thus represent a conservative estimate of the difference between the rain gauge and NEXRAD values.
Activity 6: Discussion
After calculating the differences between the NEXRAD values and the field-measured values, discussion should be held with students regarding possible reasons why departures occurred.Reasons might include: meteorological explanations for the discrepancies, such as event-specific winds or storm generating mechanisms; errors associated with rain gauges (e.g., wind); and NEXRAD precipitation estimate errors (e.g., the radar beam overshooting low-altitude precipitation).
Activity 7: Presentation Development and Reporting of the Results
Students can then create a PowerPoint presentation using a map of the field study area, the digital camera images, an example radar image, and an overlay of the NEXRAD and field-measured precipitation. Students can discuss the steps taken to reach the results, and reasons for data discrepancies.They could also describe why this project was meaningful to them during the learning process.Students can then present the results of their research in class, at a lecture series on campus, or at a local conference.
View the presentation given at the 2000 Annual Meeting of the Pennsylvania Geographical Society.

Activity 8: Assessment
There are a variety of ways that students can be assessed after completing this project.Grading criteria should be determined based on the individualized activities that the teacher requires of each student. Peer evaluation would be useful to ensure that all students participate in the grading process.Prior to the study, it may be useful to ask each students what (s)he hopes to learn from the study.Upon completion, it would be useful to survey the students to ask what segment of the project was most beneficial to them.

Suggestions and Points to Consider
• Be sure all students are trained in how to read the rain gauges to ensure that the gauges are read consistently.Creating a schedule for students so they know when they need to collect the readings (sequentially, based on the next rainfall event) would be beneficial.
• This research project is especially well suited to a team of student researchers due to the possible length of the project and the variety of methods employed.However, its length can be adjusted according to each school’s academic schedule.
• Some students may have taken courses where they have learned to use various tools or techniques useful in this study.Have them serve as mentors for the other less experienced students.
• Consider offering this project to a few students in the class as a final group project or an extra credit project.
• Consider completing this exercise as a total class project where everyone participates in at least one data collection and one data analysis activity.
• Encourage participating students to register as paper presenters at a local conference, which will motivate them to be accurate and thorough and to complete the project with a full understanding of the underlying theory and results.

Possible Modifications to the Study
• Experiments could be designed to compare precipitation estimates using NEXRAD and rain gauges in different land cover conditions, in various meteorological conditions (e.g. frozen precipitation), or in different topographic environments.
• In a meteorology course, an additional project could be conducted to assess the spatial distribution of departures between NEXRAD and rain gauge precipitation estimates drawing connections to wind direction or sky view factor above the rain gauge.
• In a hydrology course, the data could be used for water budget analysis, rainfall-runoff modeling, or to explore precipitation variability throughout a watershed.
• A number of spatial statistics could be investigated in geography or earth science courses using quantitative methods.

Example data sheet:

Watershed Precipitation Study


Site #




Official University reading

Name of Site #1

Name of Site #2

Name of Site #3

Name of Site #4

Name of Site #5


Weather conditions:
Time of precipitation:
Duration of event:

Driven by:

For further related information, access the following publications:

Cooper, J., and Mueck, R., 1990, Student involvement in learning: Cooperative learning and college instruction: Journal on Excellence in College Teaching, v. 1, p. 68-76.
Ferreri, C.P., DeWalle, D.R., Glotfelty, C.E., and Korostoff, N.P., 1997, Developing a watershed management planning class using a case study of a local watershed. In Warwick, J.J., editor, Proceedings of the AWRA annual symposium, Water resources education, training, and practice: Opportunities for the Next Century: Herndon, Virginia, American Water Resources Association, TPS-97-1, p. 491-499.
Fields, S., 1997, Weather radar starts to shape up: Earth, v. 6, p. 16-17.
Habib, E., Krajewski, W.F., Nexpor, V., and Kruger, A., 1999, Numerical simulation studies of rain gauge data correction due to wind effect: Journal of Geophysical Research Atmospheres, v. 104, p. 19723-19734.

Hunter, S.M., 1996, WSR-88D radar rainfall estimation: Capabilities, limitations, and potential improvements: National Weather Digest, v. 20, p. 26-38.
Kirk, K.B., Halstead, J.A. and Thomas, J.J., 1997, Field studies in environmental science: An interdisciplinary college course on a local watershed. In Warwick, J.J., editor, Proceedings of the AWRA annual symposium, Water resources education, training, and practice: Opportunities for the Next Century: Herndon, Virginia, American Water Resources Association, TPS-97-1, p. 501-508.
Legates, D.R., 2000, Real-time calibration of radar precipitation estimates: The Professional Geographer, v. 52, p. 235-246.
Lindsey, G., and Jewett, D., 1997, Multidisciplinary water resources education at and urban university:The Crooked Creek-Lake Sullivan research and education station.In Warwick, J.J., editor, Proceedings of the AWRA annual symposium, Water resources education, training, and practice: Opportunities for the Next Century: Herndon, Virginia, American Water Resources Association, TPS-97-1, p. 691-700.
Margraf, M.K., 1998a, Comparison of Chenhassen (MPX) WSR-88D precipitation estimates with rain gauge data for parts of Minnesota and western Wisconsin: National Weather Service Central Region Applied Research Paper No. 20-06. Scientific Services Division, Kansas City, MO, 10p.
Margraf, M.K., 1998b, Comparison of Jackson, KY (KJKL) WSR-88D precipitation estimates with IFLOWS automated rain gauge data for southeast Kentucky, Preprints of the American Meteorological Society's 19th Conference on Severe Local Storms, Minneapolis, MN, p. 461-464.
McKeachie, W., 1986, Teaching tips: A guidebook for the beginning college teacher.Eighth edition: Lexington, Mass., D.C. Heath and Co., 353 p.
Meyers, C., and Jones, T., 1993, Promoting active learning: Strategies for the college classroom: San Francisco, Jossey-Bass, 192 p.
Nespor, B., and Sevruk, B., 1999, Estimation of wind-induced error of rainfall gauge measurements using a numerical simulation: Journal of Atmospheric and Oceanic Technology, v. 16, p. 450-464.

Schratz, M., 1990, Researching while teaching: A collaborative action research model to improve college teaching: Journal on Excellence in College Teaching, v. 1, p. 98-108.
Serafin, R.J., and Wilson, J.W., 2000, Operational weather radar in the United States: Progress and opportunity: Bulletin of the American Meteorological Society, v. 81, p. 501-518.
Smith, J.K., and Lipschutz, R.C., 1990, Performance of the NEXRAD precipitation algorithms in Colorado during 1989. 8th International Conference on Hydrometeorology, Kananaskis Park, Alta, Canada.American Meteorological Society, p.184-188.
Watson, C.E., 1975, The case-study method and learning effectiveness: College Student Journal, v. 9, p. 109-116.
Woltemade, C.J., and Blewett, W.L., 2000, Development of an interdisciplinary watershed research laboratory for undergraduate education:In Higgins, R.W., editor, Water Quantity and Quality Issues in Coastal Urban Areas: Middleburg, Virginia, American Water Resources Association, TPS-00-3, p. 229-232.
Young, C.B., Nelson, B.R., Bradley, A.A., Smith, J.A., Peters-Lidard, C.D., Kruger, A., and Baeck, M.L., 1999, An evaluation of NEXRAD precipitation estimates in complex terrain: Journal of Geophysical Research - Atmospheres, v. 104, p. 19691-19703.
For questions regarding this research project, please contact Dr. Christopher Woltemade (cjwolt@ship.edu or(717) 477-1143) or Dr. Diane Stanitski-Martin (dmstan@ship.edu or (717) 477-1548).


Burd Run Interdisciplinary
Watershed Research Laboratory

Shearer Hall
1871 Old Main Dr.
Shippensburg, PA 17257

Email: cjwolt@ship.edu