Spread pattern analysis tool (SPAT): II. Examples of aircraft pattern analysis

The quality of aerial spread patterns was studied based on over 400 test runs in Arkansas during the period 1992-1997 A custom developed computer program called SPAT (Spread Pattern Analysis Tool, Grift, 2000) was used to compute overlapped spread patterns and to determine the pattern quality. The quality of a spread pattern is traditionally expressed by the average application rate (the mean of the overlapped pattern) and uniformity [expressed in the statistical coefficient of variation (cv)]. Both parameters depend highly on the swath width. Inspired by studying the cv-swath width relationships, a new measure for pattern quality called "robustness" was conceived. This parameter indicates the flexibility of a spread pattern shape, or the ability of the applicator to vary the swath width (and, hence, the application rate), either purposely or due to unintended flight path errors, and be confident that the overlapped pattern will have an acceptable uniformity. Grift(2000) stated that, as a rule of thumb, patterns with a robustness factor lower than 5% can be considered robust. From studying spread patterns of unadjusted spreaders in Back&Forth mode, it was concluded that only 3.45% of them are robust and after adjustments had been made, 2.75%. In RaceTrack mode, the percentage of robust patterns was 8.59% and after adjustments it increased to 10.28%. The majority of all patterns (approximately 70%), in both modes, had robustness factors between 5% and 15%. The results of this study imply a definite need to improve the quality of aerial application spread patterns by (I) avoiding pattern shapes that are sensitive to transforming to nonrobust, and (2) periodic calibration. The magnitude of the problem indicates that periodic adjustment of spreaders will nor be sufficient, redesign of equipment and spreading procedures may be necessary to accomplish overall high quality spread patterns.