COHSTREX 2005 Microwave Remote Sensing Measurements

The pulsed, coherent radar RiverRad was set up at the cement plant (Rinker Materials) on the bank across from Jetty Island (see Figures 1 and 3) and operated continuously from 2:36 pm on July 18 until 9:12 am on July 27. The coherent CW microwave system RiverScat became operational on the barge on the same river at 1:00 pm on July 19. It collected data for 5 minutes during all periods that the IR system was operating from July 20 through July 22.

RiverRad was operated in an azimuthally stepped mode, collecting 30 seconds of data in one-second scans from each of two antennas directed 36.6 apart. The antennas, both VV polarized, stepped 2.5 degrees in azimuth angle after each period of data collection. Thus a 50 degree azimuthal range was scanned in about 20 minutes. Because of the antenna separation, this means that a total azimuth angle of about 65 degrees was interrogated every 20 minutes. The nominal maximum range was about 425 m but will probably be somewhat less in practice due to signal-to-noise limitations. A video camera was aligned with the mean look direction of the microwave antennas and took a frame every 10 seconds. To date, the data have been processed only to the point of showing the signal-to-noise ratio as a function of range and azimuth angle on a polar plot (see Figure 9). Still to be accomplished are the extraction of calibrated cross sections and velocities from the data.

Figure 9. (left) Conical scan display produced by RiverRad. This scan shows the signal-to-noise ratio of the received signal. Land and river features are bright. The red area in the upper left is Jetty Island. (right) Video image corresponding to RiverRad scanned area showing N. tip of Jetty Island and aerial lift on barge.

Riverscat operated with two antennas, one VV and the other HH polarized. The antennas were set at a nominal 45 incidence angle and their azimuth angle depended on where the raised platform was pointing. Riverscat collects folded spectra, which means that the direction of the current will have to be inferred by other means. To date, we have extracted velocities and calibrated cross sections from the recorded spectra (see Figure 10), which will be compared with velocity measurements from the ADCP and IR data.

Figure 10. Cross sections and surface velocities produced by Riverscat during various five-minute periods. Error bars on cross sections indicate the standard deviation during the five minutes. Note that cross sections with horizontal polarization are lower that those for vertical polarization. This reduces the accuracy of velocities obtained on horizontal polarization.

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