| DESKTOP MAPPING
Program Zeroes In on Insects
Digital mapping helps Michigan County
Battle Gypsy Moths
By Kevin P. Corbley Gypsy moths in Macomb County, Michigan, hardly stand a chance of living long enough to sprout wings ever since the county went high-tech with its moth suppression program. Today, virtually every phase of the program is digital - from mapping and spraying to generating the final report - and moth control has never been more successful.
Macomb County, which includes part of the metropolitan Detroit area, is just one of hundreds of counties in the Northeastern and Midwestern United States to have established formal gypsy moth suppression programs. For more than a century these moths have ravaged hardwood forests from Canada south to North Carolina and New England west to Wisconsin.
They inflict the most damage in their caterpillar phases, eating the foliage off trees from the time they hatch in early spring until mid-summer when they enter the cocoon phase. Gypsy moth caterpillars defoliate millions of acres of trees each year, and those trees afflicted repeatedly over several years often do not survive.
Fortunately, chemicals are available to control the pests, and one of the most commonly used is an organic compound called Bacillus thuringiensis (BT). It is usually sprayed directly onto the foliage from aircraft, killing the caterpillars after they eat the treated leaves.
Through gypsy moth suppression programs in individual counties, the Michigan State University Extension Office saves thousands of acres of trees statewide each year with aerial applications of BT. Until recently, the Macomb County Gypsy Moth Suppression Program had directed its projects on paper, outlining spray areas on hardcopy maps and giving them to the pilots to hold on their laps in the cockpits.
In 1997, however, the Macomb program office learned that the county's Department of Planning & Economic Development had the technology available to make digital maps of the infestation areas, which would enable the county to take full advantage of new computerized aerial application systems being used by contractors.
The two county offices devised a way to integrate three commercial spatial data processing products - ER Mapper image processing software, MapInfo desktop mapping package, and SATLOC II aerial spraying system - to enhance the program. As a result, staff time on the program has been reduced, the accuracy of the BT spraying has improved, and precise records of each application have been made. Mapping Egg Masses
The Macomb suppression program follows treatment guidelines established by the U.S. Forest Service and Michigan Department of Agriculture (MDA). The primary goals are to maintain a certain percentage of foliage on the trees and to keep homeowner annoyance to a minimum. The Forest Service has set specific thresholds at which spraying is approved.
"We determine these thresholds by counting gypsy moth egg masses," said Lynda Billotto, program coordinator for Macomb County. "In the late summer, the female moth lays her eggs in buff-colored masses about the size of a quarter on flat surfaces out of sight."
To plan each season's BT application, Billotto and her staff survey areas that have previously been infested and neighborhoods that have initiated complaints. For an area to be targeted for spraying, the field crew must find egg masses above the threshold level in three 39.5-foot-radius plots at least 100 yards from each other within a 40-acre space.
"BT is not a preventative chemical. It only kills caterpillars that are present, so there is no point in spraying areas that aren't infested," said Billotto. Areas that qualify for BT application are called spray blocks, and the field crews mark their locations on 1"=100' or 1"=400' aerial photos supplied by the planning department. The crews also leave physical markings of the survey areas on site so they can easily be found and verified later. Billotto makes simple grid maps from the photos for submission to MDA which double checks many of the egg counts before granting spray approval.
At that time, the suppression program office is responsible for notifying all residents and property owners in the spray block that their land has been approved for chemical application. Participation is voluntary, and individual homeowners may opt not to have their yards included - a challenge to the accuracy of the mapping and spraying phases of the program. Digitizing Spray Blocks
Mapping the locations of properties where landowners object to inclusion is considered critical. Accidental spraying of objector's land can raise significant ire, not to mention potential legal action. These excluded properties are carefully demarcated on the same aerial photos as the spray blocks.
Beginning with last year's project, the program office then turned its aerial photos over to the planning department for creation of the digital maps. Department technicians scanned the photos using in-house equipment and imported the digital files using the Earth Resource Mapping, San Diego, California, ER Mapper image processing system for enhancement, mosaicking and other digital manipulation. This work was conducted on a standard Dell Pentium desktop computer with 64 megabytes (MB) of RAM.
"We decided to use our full-scale image processing system for the project because accuracy was so important," said Jeff Schroeder, an associate planner in the planning department. "ER Mapper provided us with the digital mapping accuracy needed to ensure accuracy in every subsequent phase of the project."
The locations of the spray blocks and the objectors' property lines had to be mapped precisely on the digital maps because they would be used to generate the actual flight lines programmed into the computerized chemical application system on the aircraft.
After importing the scanned photos, the technicians overlaid the files on an orthorectified SPOT satellite image of the county. They rectified the photos on screen by locating control points on the image and matching them with features on the photos. The rectified photos were automatically registered to the Michigan State Plane Coordinate System by the software.
"This is what makes the mapping exact. [With the photos in the state coordinate system,] it's easy to bring in other maps and verify we marked the blocks correctly," said Billotto. "We must be very careful not to spray properties on the edge of blocks that haven't been notified."
Once in a real world coordinate system, the photos were tiled together in ER Mapper. Its automated Edge Map and Color Balancing routines were applied to create seamless multi-scene photomosaics. Without automated color balancing, the mosaicking would have been a time-consuming manual process since the quality of the photos varied considerably because they were acquired at different times.
Even though the original scanned photos were at two different scales, the image processing system was able to convert them into a common scale for mosaicking. A total of 6 photomosaics, one for each of the major spray areas in the county, was created. Each mosaic was comprised of 4 to 7 air photos. Normally, mosaicking aerial photos on a 64 MB system is time intensive because the huge file sizes require creation of a new intermediate data file every time an enhancement routine or filter is applied. But ER Mapper uses a unique algorithm concept whereby it saves processing commands and transformation functions independently of the image data, saving disk space and completing complex processing of large files very quickly.
"Some mosaics were as large as 50 megabytes but we had no trouble applying enhancement functions to them in the image processing system," said Schroeder. Creating Flight Lines
Once satisfied with the quality of the photomosaics, department technicians displayed the data files in a desktop mapping package manufactured by MapInfo Corp., Troy, New York, using the ER Mapper MapInfo Link, a free add-on tool. This enabled them to work with the mosaics on-screen in the mapping package while the files still resided in the image processing system.
The technicians delineated vector polygons from the mosaics on screen. Vector layers were created for each spray block, with separate vectors made for every exclusion area. At this time, participants familiar with the sites would locate and vectorize streams, lakes and other environmentally sensitive areas that also had to be avoided within spray blocks. The Planning Department saved corner coordinates of the spray block and exclusion vectors as tabular text files on floppy disk. These disks were then supplied to the aerial spray company which converted the files to DXF and saved them on standard PCMCIA cards for use in their computerized application system.
For the past several years, Al's Aerial Spraying of Ovid, Mich., has handled the gypsy moth application for Macomb and numerous other counties in the state. Al's is one of a growing number of crop dusting companies to have installed a GPS-based application and guidance system manufactured by SATLOC Inc., Scottsdale, Arizona, in their aircraft.
With the spray blocks and exclusion zones entered into the system via the PCMCIA card, SATLOC converts the coordinates into a series of spray swath lines, or flight lines for the plane to follow. Inside the cockpit, a small computer screen hooked into the onboard GPS graphically shows the pilot where his plane is relative to the spray swaths.
"It's like playing a computer game," said Al Schiffer, the aerial firm's owner. "You watch the airplane on screen, fly it around and align yourself with the flight line."
When the plane enters the spray block, the pilot switches on the spray apparatus, turning it off when the computer indicates the plane is leaving the block or flying over an exclusion zone. As each line is sprayed, that swath is shaded on screen so the pilot knows exactly what areas have been covered, eliminating the possibility of repeat applications.
"This high-tech approach is a lot more accurate and much less time consuming than the old way," said Billotto.
Prior to last year, the Macomb gypsy moth office had to assemble ground crews at 3 a.m. to inflate and raise helium balloons along the perimeters of the spray blocks. These showed the pilots where to spray. Different colored balloons were tethered around the exclusion zones.
"The problem was that sometimes the balloons would be deflated by morning or they weren't high enough to show above the trees," said Schiffer. "With GPS, we spend a lot less time in the air looking for spray blocks."
Now, no ground crew is needed at the site. Outputting Spray Maps
One of the most important capabilities of the SATLOC system is its recording of flight details. With input from the GPS, it automatically plots where and when BT was sprayed and records this information back onto the PCMCIA card.
"There's absolutely no question about where the pesticide went," said Billotto.
This simplifies handling of complaints by the Gypsy Moth Suppression Program office, which sometimes gets calls from angry residents claiming their land was sprayed when it shouldn't have been or was not sprayed when it should have been.
DXF files of the actual spray locations can be taken from the PCMCIA card and saved onto floppies for direct input into ER Mapper. To generate reports on the outcome of the spray project, the Planning Department created color maps in the image processing system and printed them out to show exactly which properties received BT applications.
"The whole system is much more efficient now," said Billotto. "I would recommend our approach for any type of pest control program."
Macomb County sprayed 265 acres of residential lands in 1997. The Gypsy Moth Suppression Program office rates the program a success based on the lack of feedback from residents and reports of minimal defoliation in treated areas.
"Our office hears from people when caterpillars and moths are really being a nuisance," said Billotto. "We didn't get many calls last summer." About the Author:
Kevin Corbley is a freelance writer specializing in remote sensing, GPS and GIS. He is located in Denver and may be reached at 303-722-0312 or by e-mail at [email protected]. Back |
