Lesson Plan
Title: Comparisons of NEXRAD radar and precipitation
gauge values
Goal:
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.
Objectives:
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
Materials:
• 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.
PROCEDURES:
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.
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.
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.
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).
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
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Location |
Site # |
Date |
Time |
Precipitation/Radar
(inches)
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Official University reading
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Name of Site #1 |
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Name of Site #2 |
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Name of Site #3 |
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Name of Site #4 |
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Name of Site #5 |
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Etc. |
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Weather conditions: Time of precipitation: Duration of event: |
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Observers: Driven by: |
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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.
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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.
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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).