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Data collected with AN/TPS-71 radar has been used to validate the RADARC model. For the first ten days of January , April, and July, noon and midnight, the vertical ionograms, oblique backscatter soundings, radar ground backscatter amplitudes and noise levels have been compared with Model predictions. The differences between the Model and median ionospheric soundings are small enough to have negligible effect on predictions. The coverage predicted for oblique backscatter soundings agrees well with observed median data except for sporadic E effects which were under-estimated. Medians of observed ground backscatter agree fairly well with predictions. The actual noise that controlled radar performance was the most significant deviation from the model; all nighttime and January day noise was higher than that predicted; and this was due to 'multiplicative' noise.... Ionospheric Models, OTH RADAR, Skywave Transmission

The expected performance of high-frequency radar has been examined as a function of sunspot cycle, season, and time of day, using recent ITSA techniques. The method of performance assay provides a good basis for both radar design and comparison. A particular set of radar parameters was chosen: PG squared T sigma = 137 db (where P = average power above a watt, G = antenna gain above an isotropic radiator in free space, T = predetection integration time over a second, and sigma = target radar area over a square meter) and a 10- db postintegration signal-to-noise ratio is required. A 5-to-1 frequency band permits effective operation at distances from 500 to 1500 naut mi 95 percent of the time, to 1900 naut mi 80 percent of the time, and to 2000 naut mi 60 percent of the time. The sporadic E effects have been ignored, which makes long-range coverages optimistic. The better coverage long-range limit is generally set by the maximum one-hop distance. Vertical launch angles between 0 and 38 degrees are useful. Performance improvement possibilities have been examined; it is estimated that 20 to 40 db over the postulated 137 db could be achieved.

Aircraft, ship, and clutter echoes have been studied using surface- wave propagation on the Chesapeake Bay. These studies show that coherent pulse doppler methods can be used for surface target detection. Required radar features for several applications can be estimated.

Techniques are described for the prediction and analysis of OTH radar operation. A complete ionospheric description is included and optimal computer techniques are utilized to give a practical means to handle the frequency- and antenna-scan management of the radar. Actual data are analyzed to show how the backscatter response from one frequency radar sounding can be used to derive the actual transmission-path characteristics that need to be known for effective radar operation., Prepared in cooperation with the Office of Telecommunications, Boulder, CO.