Wildl. Soc. Bull 22:674-676, 1994 WILDLIFE SOFTWARE NAVIGATING, AERIAL TRANSECTS WITH A LAPTOP COMPUTER MAP R. MICHAEL ANTHONY, Alaska Fish and Wildlife Research Center, National Biological Survey, 1011 East Tudor Road, Anchorage, AK 99503 ROBERT A. STEHN, Alaska Fish and Wildlife Research Center, National Biological Survey, 1011 East Tudor Road, Anchorage, AK 99503 Key words: aerial survey, global positioning system, GPS, line transect, remote sensing, wildlife software The broad coverage of the global positioning system (GPS) can provide location information with 15-100 m accuracy for navigation and natural resource management. It is especially valuable in remote areas like Alaska where there are few landmarks. GPS receivers connected to portable computers can record intermittent position information for mapping the flight paths of aircraft (Bobbe 1992, Evans 1992) and provide real-time aircraft locations on moving maps to assist pilots in navigation. We wrote a PC BASIC program (GPSTRACK) that incorporated aircraft locations for post-flight analysis and real-time display of aircraft position to aid in navigating predefined transects. This program has improved the precision of navigating transects and the efficiency of conducting our aerial surveys. Improved geographic positioning was especially useful for closely spaced, narrow strip transects used to sample colonies of black brant (Branta bernicla nigricans) with a video camera. GPSTRACK uses RS-232 input from a GPS receiver to display the current aircraft location as the point of an arrow on a map on the computer monitor, updating the location every second. The map is located in a window that also displays the transect as a solid line and a lead-in as a dotted line, which aids in locating transects and in approaching the beginning of transects at the correct heading (Fig. 1). The map is initially oriented north, but it can be re-oriented repeatedly to match the direction of the aircraft, allowing easy interpretation by the pilot and navigator. Transects are defined by the beginning and ending coordinates stored in an ASCII text file, and the longest transect defines the initial map scale. There is no practical limitation on the number of transects in the record file, but programming restrictions currently limit the number to 1,000 with a 5-digit identification code. A variable-size grid is displayed over the map as a reference to scale. Landmarks may be displayed through optional ASCII text files containing the location of geographic points or boundaries in the vicinity of the transects. Users can "zoom-out" from the window to aid in transect location or "zoom-in'' to improve the precision of navigating the transect. At a user-defined interval, the computer stores flight path information to an ASCII text file. Output records contain the record number, transect number, time (hr: min: sec), seconds from midnight, flags indicating the location of objects of interest, Universal Transverse Mercator (UTM) x-coordinate, UTM y-coordinate, degrees and decimal minutes longitude, and degrees and decimal minutes latitude. The coordinate values stored are based on the UTM zone in which the first transect originated so that crossing zone boundaries does not require special calculations of locations among zones. Fig. 1. Computer display windows created GPSTRACK program showing a transect that traverses an island. Path of an aircraft approaching and following transect 45 is represented by the solid curved line. Abbreviated instructions for using the program are displayed in the upper left window. Longitude and latitude from the GPS receiver are shown in the lower left corner. Other features are for special situations. One feature allows the aircraft to leave in the middle of a transect by marking the point of departure and terminating flight tracking. Either 1 or all transects can be displayed. Nine user-defined hot keys are used to record locations of wildlife observations or other objects of interest in the aircraft location file. A tenth hot key allows storage of an 8-character text string with the location records. A simulation mode is available for examining landmark and transect files, to aid in pre-flight planning, and to plot flight paths from output files after survey flights. GPSTRACK runs on computers operating under MS-DOS (Microsoft Corporation, Bothell, Wash.) with a central processing unit (CPU) clock frequency--8 megahertz with 640 kilobytes random access memory (RAM) and an RS-232 serial port. A hard disk and faster CPU are recommended for acceptable operating speed. The program uses a CGA or VGA monitor (color or monochrome). Input parameters allow use with a Trimble Navigator GPS receiver (Trimble Navigation, Sunnyvale, Calif.), Trimble Pathfinder, Navstar XR4-G (Navstar Electronics, Sarasota, Fla.), and other receivers with National Marine Electronics Association (NMEA) output formats 0183 or 0184. Input parameters can be modified for compatibility with other receivers, but the executable version of the existing program will operate only under the described conditions. True BASIC (True BASIC, Inc., West Lebanon, N.H.) communication library and language system software are required to modify the GPSTRACK program code. Although the program was written to aid in navigating transects, it also can track flight paths and record locations of wildlife or other objects during other aerial activities. GPSTRACK is available from the authors by sending a 3.5 or 5.25 inch formatted diskette and self-addressed label or through the Bird Monitor bulletin board (301-498-0402). LITERATURE CITED BOBBE, T. 1992. Real-time differential GPS for aerial surveying and remote sensing. GPS World 3:18-22. EVANS, D. L. 1992. Using GPS to evaluate aerial video missions. GPS World 3:24-29. Received 19 March 1993. Accepted 29 April 1994. Associate Editor: Rexstad.