Experience in the Field

Rockland County, New York

In an effort to control the spread of West Nile virus, Rockland County, New York, is using color infrared (CIR) aerial photography to assist in identifying and treating mosquito breeding grounds within the County's municipal boundaries. As part of its public health and environmental management programs, the County contracted Sewall in spring 2001 to capture photography of the 176-square-mile area at a scale of 1"=750' during the months of April and June. Following the aerial missions, Sewall scanned the CIR film at 750 DPI and plotted out 30"x30" large format prints for the County Health Department to use in locating wetlands, swimming pools, catch basins, and other hydrologic features that have a high probability of breeding mosquitoes. Sewall also produced 9"x9" contact prints from the film. On the basis of the photo interpretation, County officials last summer conducted site tests, interviewed citizens, and applied larvicide to selected open water breeding areas to control mosquitoes during the larval stage. This effort was in conjunction with a comprehensive mosquito surveillance and control program, which has included educating the public on virus prevention, testing individuals, and collecting and testing dead birds.

In addition to mosquito control, the County is using the photography to identify other potential problems in the environment, including underground pollution, stream discharges, and tire dumps. Under the auspices of the Planning Department, which is developing an enterprise-wide parcel-based GIS, County officials plan to provide all County departments and the public with on-line access to the photography in digital format.

According to Health Department Engineer Joseph Puchalik, high-quality, high-resolution aerial photography "gives us visual access to areas not readily visible from public roads because of vegetative cover or terrain features." As an interpretative tool, it dramatically "reduces the area that must be covered on foot and the number of man hours in the field."

The April photography, acquired before trees leafed out, enabled the Department to locate wetlands, swimming pools, and other bodies of water with a high probability of breeding mosquitoes. This photography was also useful in identifying the relative location of structures with vulnerable populations, such as the elderly in nursing homes and children with immune-deficiency diseases. Changes of water color and tone detected in the summer photography signaled algae buildup in unmaintained swimming pools and other areas of standing water, which can be ideal mosquito breeding habitat.

This information provided the basis for the County's work with the public last summer to eliminate potential breeding areas and to treat 26 selected sites with larvicide by helicopter. As of June 2003, there are no reported human cases of West Nile virus in the County. In New York State, the Centers for Disease Control and Prevention report 82 lab-positive human cases of West Nile virus with 5 deaths (out of 4,156 cases with 284 deaths nationwide).

Mr. Puchalik says the County is also using the photography to prevent and manage other environmental hazards, such as leaking underground tanks. "CIR is an early warning system." Underground pollution affects tree leaf color: "Trees that show stress are not a deep red, but pink, orange, and white." With the photography, "we can identify the possible presence of leaking tanks from nearby gas stations or chemical plants." Color changes in streams and other bodies of water can indicate pollutant discharge also.

Rockland County consists of five towns and 19 villages in lower New York State with a population of over 288,000. The area borders the Hudson River to the east, the State of New Jersey to the south, and the Ramapo Mountains to the north and west.

For more information on this project, please contact Lisa Schoonmaker at 207 827 4456; E-mail: schl@jws.com

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