On the Space.com bbs I posted some links to possible MGS images of ice covered rivers or streams on Mars:

Ice rivers on Mars.
http://uplink.space.com/2/OpenTopic?q=Y&a=tpc&s=874094803&f=684094803&m=7933030356

Calliarcale a moderator on the bbs pointed me to some images of Earth:

Cryosphere -- Snow/Ice
http://visibleearth.nasa.gov/Cryosphere/Snow_Ice/

I think I'll need some images at higher resolution, say at the 1-10 meter scale, than the ones shown here.
But I might have found on one of the pages something even better than images to compare to.

On this page:

Snow and Ice Storm in the Midwest
http://visibleearth.nasa.gov/cgi-bin/viewrecord?11814

there are images of the same scene in both visible .645 microns and near-infrared 1.6 microns wavelengths.
The description of the images states:

"The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra satellite produced an image of the area on February 1, 2002. In visible wavelengths (above, top) the ice appears transluscent, in contrast to the bright white snow and darker ground. The ice is visible as a thick black stripe along the lower right edge of the medium gray snow in the near infrared image (above, lower). Because water absorbs near-infrared light so strongly, bare ground is actually brighter than the snow in this image."

I believe what this passage is saying is that the bare ground contains liquid water and in the bottom near-infrared image the bright area on the right is this bare ground containing liquid water.
You'll note there is a difference in how the snow, ice, and bare ground with water appear in the two images.
Then this may provide a means to determine both clear ice covered ground and ground containing liquid water on Mars.

The Hubble Space telescope is able to make observations at these visible and near-infrared wavelengths:

Martian Colors Provide Clues about Martian Water
http://oposite.stsci.edu/pubinfo/pr/1999/07/

It is notable here as well that Hubble scientists regard it as important to obtain visible color images of Mars:

"Accurate colors are needed to determine the composition and mineralogy of Mars. This can tell how water has influenced the formation of rocks and minerals found on Mars today, as well as the distribution and abundance of ice and subsurface liquid water. Confirmation of the presence of certain oxidized (rusted) minerals (processed by heat or water action) would imply the possibility of different, perhaps much more Earth-like, past Martian climate periods. Because the smallest features visible in this image are only about 14 miles (22 km) across, Hubble can track small-scale variations in the distribution of minerals that do not follow global trends. The image was generated from three separate Wide Field and Planetary Camera 2 images acquired at wavelengths of 410, 502, and 673 nanometers, in March 1997."

The TES spectrometer also appears to be able to measure these visible and near-infrared wavelengths:

MGS Thermal Emission Spectrometer
(Optics arrangement)
"To measure the brightness of reflected solar energy, a third sensor views the planet in the 0.3 to 2.7 micron region. Each sensor has six detectors arranged in a 3 by 2 array, each with a field of view of 8.3-mrad. This translates to a spatial resolution of 3 km from the MGS orbit."
http://emma.la.asu.edu/MARS_SURVEYOR/MGSTES/inst_description.html

However, judging from the listed wavelengths it measures I don't think THEMIS has the capability to detect the 1.6 micron wavelength.

The OMEGA infrared spectrometer to fly on the Mars Express orbiter is also expected to be able to distinguish between the different phases of water on Mars.

See:

DISCRIMINATION BETWEEN SOLID, LIQUID AND GASEOUS H2O, AND
ASSESSMENT OF H2O TEMPERATURE BY SPECTROSCOPY USING THE OMEGA
IMAGING SPECTROMETER (MARS EXPRESS).
Bernard SCHMITT, Sylvain DOUTÉ, Stéphane ERARD, Yves LANGEVIN, Jean-Pierre BIBRING.
Laboratoire de Planétologie de
Grenoble, CNRS - Université J. Fourier, France;
Institut d’Astrophysique Spatiale, CNRS -Université Paris-Sud, Orsay, France.

in:

MARS INFRARED SPECTROSCOPY:
FROM THEORY AND THE LABORATORY TO FIELD OBSERVATIONS
June 4-6, 2002
at the Lunar and Planetary Institute
LPI Mars Spectral Workshop II (2002)
p. 45.
http://www.lpi.usra.edu/science/kirkland/Workshop2/report_workshop2.pdf

Bob Clark