Az, za dependence of radar signals in dome

april 2003

    The azimuth, zenith  dependence of various radars was measured on 27mar03 during the day.
radar freq rotation bandwidth duty cycle (1 freq)
FAA 1350 12 secs 200 Khz 5usec/2500=.2%  
remy  1290 12 secs 200 Khz 5usec/2781=.2%  
aerostat 1256 11.6 secs 1.6 Mhz 160/3200=5% only on for 1 azswing
fps117 multi 12 secs 1.6 Mhz 51/1500 = 3.4%
freq hopping. The duty cycles are only for the
number of pulses until the next hop.

Taking the data:

 Azimuth swings were done at .2 degrees/sec between  az=270 and az=630. After each swing the zenith angle was stepped by 2.5 degrees. The measurements covered za's of 2, 4.5, 7, 9.5, 12, 14.5, 17, and 19.5 degrees za alternating the azimuth direction. Data was taken with the correlator sampling at 1 second. 25 Mhz. 1024 channel,   9 level spectra were taken centered at :1405,1350,1290, and 1258 Mhz.

Reducing the data:

    All of these are pulsed radars with rotation rates of about 12 seconds. The strength of the radar changes as it rotates around. The 1350 and 1290 radars are at peaks when they point at us. The aerostat and punta salinas radars blank their signal when they point at us (but the time right before/after the blanking is usually the strongest).
    The first plots show the max and average of the spectra for each azimuth swing. This shows the general shape of the pulses.
    The 2nd and 3rd set of plots are made at the resolution of the sampled data (25 Khz) and a second set averaging the radar pulse over its  transmitted bandwidth.  Sets of 12 seconds (1 rotation) were taken at a time and the peak value (for both bandwidths) divided by the median system temperature for the az swing were plotted versus azimuth angle. This gave an azimuth resolution of 12 secs *.2 deg/sec or 2.4 degrees in azimuth.

A few comments on what exactly has been measured.

    We are not able to measure the actual power of the radar pulse with the 1 second integrations of the correlator. The radar data has been way under sampled. The duty cycle of the FAA radar (1350 only) is .2%. That means the integrated pulse is smaller by a factor of 1/.002= 500 than what it really is. The radars are probably also saturating the system when the pulse is on and pointing at us. A very strong pulse may appear as a weak pulse if it has driven the system so far into saturation that you end up getting negative gain.

FAA 1350 Mhz radar plots.

    The FAA radar is a dual frequency (1330,1350) Mhz radar with a pulse width of 5 usecs. The two pulses are separated by about 6 usecs. The radar itself is situated east of us.

    The wider band shows a small 3 azimuth variation. The peaks change with za. They also do not line up with similar 3az term with the 1290 remy data. Since the data was taken at the same time, it is probably not something like the sun (unless the peaks are frequency dependent).

REMY 1290Mhz radar plots.

    This radar transmits a single frequency 5 usec pulse. It is located west of us at the end of the runway at remy airport (but it is used for monitoring drug smuggling).

Aerostat 1256 Mhz radar plots.

    This radar is on a tethered balloon about 5000 feet (???) up over lajas (southwest of us). It has a dual and quad frequency mode. It blanks its transmitted power +/- 20 degrees about our direction. When the weather gets bad it has to be lowered to the ground. It was transmitting during the za=2 and part of the za = 4.5 azimuth swings.

za dependence of 1350,1290 radars.

    The plot shows the zenith angle dependence of the 1350 and 1290 radar. The data was smoothed in frequency to 225 khz and the averaged over each azimuth swing. The dotted lines show tsys vs za (with no radars). There is a small increase with za and both radars show as jump up at za=19.5.


processing: x101/030327/