14apr12 Tsys increase during rain.
Project a2335 was observing with lbw on
14apr12 from 19:00 to 23:00 ast. They did 300 second on, off
position switching using the interim correlator. They used
frequencies between 1350 and 1400 MHz. When reducing the data, a
number of on,off pairs had baselines with variations that extended
across the entire 25 MHz band. This occurred for both pols. It also
occurred in the 4 subcorrelators that were used. During this
observation there was some rain. By plotting the on/off-1 vs hour
and then over plotting the cumulative rainfall, you can see
that the baseline variations are correlated with the rainfall.
on/off-1 position switching with the cumulative rainfall over
plotted (.ps) (.pdf):
- The black lines are the 5 minutes on/off -1 position switching
- They did 16 on/off pairs (11 minutes each)
- I've spread the on/off-1 over the 11 minutes of time (5
minutes on , 1 minute move, 5 minutes off).
- The blue vertical lines show the start of each on/off -1.
- The red lines show the cumulative rainfall in inches for the
day. This is taken from the weather station on the
- the baseline variations are during or precede rain fall.
- The weather station records water as it hits the
- The radio waves will be affected by water in the atmosphere
so there can be a delay from the radio wave instability to the
arrival of rain.
- When the rainfall stopped, the baselines stabilized (hours
21.2 to 22.1)
- rainfall rates of about .15 inches / hour caused
baseline variations of about 2% of Tsys(about 30 or .6K)
- looking at the weather station and a2335 data: