SPREAD PATTERN ANALYSIS TOOL (SPAT): II. EXAMPLES OF AIRCRAFT PATTERN ANALYSIS

Abstract

The quality of aerial spread patterns was studied based on over 400 test runs in Arkansas during the period1992-1997. A custom developed computer program called SPAT (Spread Pattern Analysis Tool, Grift, 2000) was used tocompute overlapped spread patterns and to determine the pattern quality. The quality of a spread pattern is traditionallyexpressed by the average application rate (the mean of the overlapped pattern) and uniformity [expressed in the statisticalcoefficient of variation (cv)]. Both parameters depend highly on the swath width. Inspired by studying the cv-swath widthrelationships, a new measure for pattern quality called robustness was conceived. This parameter indicates theflexibility of a spread pattern shape, or the ability of the applicator to vary the swath width (and, hence, the applicationrate), either purposely or due to unintended flight path errors, and be confident that the overlapped pattern will have anacceptable uniformity. Grift (2000) stated that, as a rule of thumb, patterns with a robustness factor lower than 5% can beconsidered robust. From studying spread patterns of unadjusted spreaders in Back&Forth mode, it was concluded thatonly 3.45% of them are robust and after adjustments had been made, 2.75%. In RaceTrack mode, the percentage of robustpatterns was 8.59% and after adjustments it increased to 10.28%. The majority of all patterns (approximately 70%), inboth modes, had robustness factors between 5% and 15%. The results of this study imply a definite need to improve thequality of aerial application spread patterns by (1) avoiding pattern shapes that are sensitive to transforming to non-robust,and (2) periodic calibration. The magnitude of the problem indicates that periodic adjustment of spreaders willnot be sufficient, redesign of equipment and spreading procedures may be necessary to accomplish overall high qualityspread patterns.