17apr05 sband bistatic radar run has pointing trouble



    A moon bistatic radar run was done between arecibo and the gbt using the sband transmitter on 17apr05 (starting about 18:25 ast).  The telescope was pointed at the south pole of the moon. When the data was reduced, the ranges near the south pole saw a large variation in the signal to noise. After about 30 minutes (??) the signal to noise started to drop. This continued until  it was about 10db worse toward the end of the observation. The observation was restarted at 18:45 ast.

    Since no data was recorded at arecibo, there were no headers containing the positions to compare with the ephemeris file. The encoder values (that are independently archived once a second) were used to compare with the ephemeris file. The computations done where:

The model removal was not perfect because  the model was evaluated at the encoder azT, zaT and not (az-modellaz, za-zamodelerr). This introduced a small error.

The plots show  17apr05  the actual and requested positions (.ps)  (.pdf):

So what happened??

    It looks like the rate was not getting updated for the telescope. This could happen if


    The next day a similar run was done. The plots show  18apr05  the actual and requested positions (.ps)  (.pdf):.
The only problem on this day was when the zenith angle went below 2 degrees za (the keyhole).