Testing for Side Lobes in the SPARO/Viper Beam
The basic idea of this test is to determine if there are any large
side lobe components of the sparo beam. Basically, it is a rough
first order test to see if our beam shape is close to that desired.
The idea is to point Viper at the moon and then step off in 12' steps up
to 3 degrees in each direction in both elevation and azimuth, checking to
see if a moon signal can still be seen at such large angular distances.
The moon has a flux of 1.5*108 Jy if it is considered to be
30' in extent at a surface temperature of 200 K. If we observe the moon
at 18 degrees elevation with a 450 micron zenith opacity of 1, we will
have an NEFD of 900 JyHz-1/2 in the best case. In the worst
case, which would be 7 degrees elevation and zenith opacity 1.5, we will
have an NEFD of 3.1*105 JyHz-1/2.
We want to spend a relatively small amount of time on side lobe testing
and still be able to come away with a meaningful result. If we take 5
steps per degree, and 40 seconds of integration time per step, we can
scan through 6 degrees in 20 minutes (divided by the duty cycle). For the
best case, we will achieve an effective noise of 140 Jy during these 40 second
integrations. This would allow us to test for extended structure in the
SPARO point spread function down to 60 dB. It also allows us to look
for spikes in the PSF down to about 47 dB. In the worst case we would have
a noise of 49,000 Jy, allowing us to test for extended structure in the
PSF down to 35 dB, and look for spikes in the PSF at the level of 22 dB.