I thought I'd start this thread for SHARAD. Today's release at the AGU Fall meeting had three SHARAD-related products (1, 2, and 3).

Am I correct in assuming that the surface is the brightest reflector towards the top of the image?

And does anyone have simulated views of what subterranean liquid water might look like?

Thanks!

Does anyone know how SHARAD's capabilities differ from those of MARSIS? (The MARSIS website is profoundly unhelpful for figuring this out.)

MARSIS is lower resolution but deeper penetration. SHARAD is higher resolution but shallower penetration

Doug

Emily's latest blog entry reminded me that I should have provided links to the respective Planetary Photojournal pages to give context for the observations: PIA09074, PIA09075, PIA09076.

Today the Feb issue of Ciel & Espace arrived and there is a short message about MARSIS. If I try to summarize and translate the French language correctly:

“The MARSIS radar stands dry a little bit.
Lots of buried craters detected since start of work in summer 2005. But its real mission is to look for liquid water deeper down, and why hasn’t that been found yet? Answer: the radar doesn’t penetrate as deep as expected because of the high levels of Iron encountered in the Martian soil. This effect was underestimated in the original development (modeling) of MARSIS. The result is that MARSIS doesn’t probe deeper than some 4000 m in those areas where the instrument is targeted to look for (deep) liquid water. After 1 ½ year the chances of it striking lucky are now becoming smaller. Still, MARSIS has only probed some 20% of the total surface area and - who knows - at some places the liquid water may be closer to the surface than foreseen.”

This feedback gives some perspective to Dougs message above. Let's hope that SHARAD is not equally affected by higher than foreseen Iron levels (same designers).

Possible problems with MARSIS penetration depth and the geoelectrical properties of the martian subsurface have been feared for quite some time. As far back as the GeoMars 2001 conference. In fact, look under the conference's Resource and Background Documents link and scroll down to "RELATED PUBLICATIONS" for some good references.

The conductivity of the ground affects radar at all wavelengths but it gets worse at shorter wavelengths.

At any given wavelength, you have a "law of dimimishing returns" in trying to probe deeper against attenuation. It's double-whammy .. attenuation on the way in, attenuation on the way back out. The off-vertical clutter and system noise eventally eat your lunch.

Ultimately, you will want to go with an expen$ive dedicated spacecraft with high wattage radar sounding and non-trivial antenna designs that maximize vertical sounding energy into a relatively narrow beam (HARD at long wavelengths) and suppress off-vertical reflections more than with Sharad and Marsis.

Yes, but I'll remind y'all that the Soviets used to fly high-power radarsats to track U.S. naval movements, and their power requirements were so high that they were equipped with nuclear fission piles. It was one of these satellites that crashed in Canada and spilled plutonium over the countryside.

It's rather difficult to get the raw power you need for such powerful radars with solar or thermoelectric power sources...

-the other Doug

Even more so in Martian orbit... I think the US could build a safe nuclear reactor, but the masses have contantly protested such a thing, the most recent being the Prometheus class spacecraft...

It was mostly uranium and fission products, not that these are much more pleasant to spill over the countryside than plutonium.



New space nuclear reactors could be built, given sufficient funding. Prometheus was killed not because the masses protested (there was no mass protest), but because it was so ridiculously expensive in the current fiscal climate.

Back on topic, what are the applications of high powered radar for scientific research that is not possible with techniques like SAR and other processing? For the military, high power buys resolution in a short time interval. What would be some science data that high power will get vs. integration over motion and time?

Essentially penetration. SAR is very good for improving resolution beyond what is normally possible with the relatively large radar wavelength, but no amount of processing can bring out data that isn't there.

Comparison with the Soviet radar satellites isn't fair. Those were meant to cover wide swaths of ocean, the signals had to pass twice through Earth's thick atmosphere and the targets were likely to use countermeasures.

tty

NASA Satellite Finds Interior of Mars Is Colder

Spectacular animation of MRO scanning the North Pole