[X] My Assistant

[tasp]

I recall seeing a fairly technical article some years ago (probably longer ago than I might want to admit) on phased array military radar techniques.

One of the 'tricks' discussed was slowly ramping the frequency of the transmitted radar beam, and then in the receiver electronics having a corresponding frequency change in the pass band allowed into the amplifier stages.

The result was a tremendous increase in the S/N ratio of the system. You are essentially integrating the power of the radar beam over the time it takes for the frequency to change, and this assumes all your noise sources stay constant.

The technique presumes you have at least an idea regarding the arrival time of your echo, so the received signal is in the pass band at the right time.

I am wondering if anything like this has been applied to asteroid studies, or even more distant objects.

Perhaps combining this technique with (IIRC) the Planetary Society's special SETI receiver electronics Paul Horowitz developed.

If I understand that gadget, it just regularly samples a wide range of incoming signals, and bins the amplitudes of all the received frequencies of interest.

Perhaps that gadget could be used to analyze the return echo from the ramping frequency radar beam. It doesn't 'care' about having a pass band synchronized to the transmitted signal to object lightspeed delay, so with this set up, we do not presume a range for our, as yet, undiscovered object. We just need to analyze the data Horowitz's receiver generates.

I would suggest this system be operated to detect objects in opposition (as seen from earth) so we have a minimal approach/recession velocity to mess up our computed distance to any thing we find.

A limitation of this is you will find objects very accurately in range from earth, but rather poorly located perpendicular to the direction of the beam. I am guessing you get about a 1 degree circle to look for your very accurately distance measured object.

I am not a whiz with math, but it seems if you wanted to drastically increase the range of this system, you just ramp the transmitted beam frequency more slowly. You would probably be limited to a maximum ramp time of 10 hours or so, for a radar dish on the earth's surface.

It may be possible to 'add' observing runs from day to day too.

For a radar with a beam power of 360,000 watts/sec, with a 1 hour 'exposure' (ramp time) you have the equivalent (maybe) of a radar beam with 12,960,00,000 watts. Go to 10 hours, and it is 129,600,000,000 watts.

(I am not volunteering to pay the electric bill for this)

These are rather dramatic possible increases in radar power. If you run this thing for 10 days (do oppositions last that long?)
you square the power of the example beam.

This might be an interesting technique to do periodically. You are essentially sampling to great distance, all objects large enough to detect at a given range. Note your receiver will need to be geographically separated from your transmitter. Light time delays out to the limits of detection with this technique might be hours (dare I hope?) and you want the receiver on the the right side of the earth when the most distant detectable echoes come back. It would be interesting to have an exhaustive census of solar system objects in a sampling of areas.


{If this is already in the works, cool! If someone else has looked into this and it won't work, well, piffle!}

[siravan]

IIRC, the technique of ramping up the frequency of radar pulses in order to improve range resolution is a very common one and is called "chirp modulation" (http://en.wikipedia.org/wiki/Chirp). I guess most space applications of radar already use it (e.g. SHARAD on MRO).