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Ground speed data is used as an input to automated control systems for application of high cost farm inputs. The benefits of accurate ground speed information are precise control of planting / spraying operations, accurate position detection, and implement performance optimization. Presently, radar ground speed measurement systems are commonly used due to reasonable cost and acceptable accuracy. The objective of this study was to identify and evaluate the issues related to ground speed measurements under varying vegetative covers and ground conditions. Empirical field observations indicate that radar ground speed measurements show increased error as crop vegetative cover / height increases. A low cost GPS based ground velocity sensor has recently been developed, and that system was compared to the other speed sensors. These systems were compared to a reference (true) ground speed. The experimental study included instrumentation of a tractor with speed sensors and a data acquisition system. Preliminary speed measurements were collected for varying vegetative covers of different crop heights and were evaluated to determining any deviations of radar speed measurements as compared to the reference speed. Results included validation of GPS and radar data for true ground speed measurements in terms of their accuracy.