Figure 1. Standard UND Doppler radar output
1. Introduction
Severe weather affects all aspects of the human
and natural environment. The ability to assess the affects of
severe weather from archive data or the ability to project path
and extent of severe weather on the natural or human environment,
in near real time, from integrated Doppler radar data and GIS
vector data would provide tremendous benefits to a broad and diverse
segment of society.
Government agencies would derive virtually unlimited benefits from the ability to assess and quantify the effects of heavy rains, strong winds, and hail events. The ability to locate, in real earth coordinates, the path and area extent of a particular severe weather event would allow county and city officials to dispatch appropriate government resources to assess the nature of the event and provide immediate emergency services to the affected area. State and federal agencies would now have reliable data on which to predict or assess the effects of heavy rain events relating to river flooding. Public service carriers could be warned of potentially dangerous sections of roads or rail that have experienced severe weather events within the last few minutes. Private citizens would also benefit from access to timely, accurate and geographically located information relating to severe weather events. Travel plans could be rerouted or postponed based on severity of the event. Local city programs could provide a more timely and accurate postponement of scheduled events based on field conditions and location of storm event saving wasted time and trips to canceled events.
The key to providing severe weather and GIS related information for use by a broad spectrum of users is the ability to accurately locate the size, track, and severity of a storm event.
The Regional Weather Information Center is currently working
on Doppler radar and GIS data integration. Initial research has
indicated that fusion of Doppler weather data and GIS related
information can provide a accurate assessment of the location,
severity, and type of weather event.
2. Background
Weather radar depicts the intensity of a storm by
correlating the power sent out from the radar to the power received
from an object that is able to scatter part of the energy back
to the radar site. In the case of precipitation or hydrometeors,
the stronger the power returned correlates to an increasing number
of particles within a sample area, light rain vs. heavy rain,
or to the size of the hydrometeors, raindrops vs. hail stones.
These returned values are represented by a reflectivity scale
measured in dBZ as depicted on the scale in the lower right hand
corner of the UND Doppler radar image (figure 1).
The reflectivity scale is logarithmic therefore
values on the left side of the scale represent weak echo in the
form of non precipitating events to light rain, to values on the
right side reach will range from light rain to heavy rain and/or
possible hail.
3. Case Study
On August 16, between 6:30 PM and 9:30 PM a line of heavy convective thunderstorms passed through the Grand Forks area. Heavy rain, strong winds, and hail were associated with this weather event. Property damage was reported with agricultural crop damage the primary loss. The UND Doppler radar was in time mode operation during this particular event and recorded image scans of the same area every five minutes. The data was stored on tape backup archive for latter use.
As part of a ongoing research effort at the Regional
Weather Information Center a team of radar scientist and Geographic
Information systems experts gathered field information on the
location, extent, and severity of this event. Data gathering consisted
of anecdotal information gathered from local farmers, field sampling
using GPS, and supporting information from local crop adjusters.
The raw radar data was retrieved from tape and processed for
use (figure 2).
Doppler radar data and associated base map data is not conducive of accurate determination of location information associated with convective storm events. Registration of Doppler digital data to geographic information systems data allows detailed location information to be applied to the storm event. Calculations on extent and path of potential damaging storm events can now be analyzed and presented in graphic format (figure 3).
Vector analysis of the storm event on the evening of August 16, 1996 provides accurate location and distribution information. Figure 4 depicts the movement of the storm cells over a five minute period of time and illustrates the probable storm tract and extent of probable damage. Post-storm data gathered using global positioning systems, farmers reports, and hail adjustment reports indicates that the location error associated with Doppler radar data and GIS data integration error is extremely low.
Variability within the storm track polygon suggest
that the five minute scanning strategy does not allow for detailed
determination of damage assessment for the entire area associated
with the storm track polygon.
4. Conclusions
Integration of Doppler data with geographic information systems data provides the location information necessary to generate detailed and accurate post-storm damage assessment. While it is recognized that detailed information on the severity of the damage within the storm track polygon can not be determined with any degree of certainty, GIS data integration provides the location information necessary to identify the sections along the storm tract axis that have the highest probability for crop and property damage. This type of information will provide farmers and insurance adjusters with map products that depict the probable location of damage to crops related to hail or excessive precipitation events associated with convective storm events.
Last modified 03/97.