Conference 7.286::space

752.0. "NASA project to measure changes in Greenland's polar glaciers" by PRAGMA::GRIFFIN (Dave Griffin) Tue Aug 20 1991 21:33

RELEASE: 91-133 (8/20/91)

     Researchers from the NASA Goddard Space Flight Center's Wallops Flight
Facility, Wallops Island, Va., will use satellite and airborne instruments to
measure the surface elevation of polar glaciers, aiding scientists in
determining ice buildup or melting due to global climate changes.

     The campaign, which will take place in Greenland between Aug. 23 and Sept.
16, will use the Global Positioning System (GPS) and a laser-ranging instrument
aboard a P-3 Orion aircraft to accurately measure the elevations of the glacier
surface.  The laser will scan an area 656 feet wide immediately below the
aircraft, measuring the elevations of the glacial surface to a target accuracy
of 4 inches, said Bill Krabill, Principal Investigator from Wallops. Other
instruments on the aircraft will include two radar altimeters, a profiling
laser and an inertial navigation system to measure the aircraft's pitch and
roll.

     "Knowledge of the ice budget in polar glaciers will provide an indirect
measure of sea-level changes and may indicate trends in world climate," said
Krabill. It has been estimated that a 9-inch change in the average height of
the central Greenland ice sheet would result in a 0.12-inch change in the sea
level of the world's oceans.

     Some computer climate models show that increased global temperatures would
partially melt polar ice sheets and raise sea level.  Other models show that
rising temperatures would stimulate increased precipitation that would, in
turn, increase the size of ice sheets.  Following several decades of
international field investigations, scientists need to gather more data about
the ice surface elevation to determine whether ice sheets in Greenland or
Antarctica are growing or shrinking.

     Measuring large ice sheets may be a more practical method for helping
assess changes in sea level, which is difficult to measure directly.  However,
measuring these sheets using ground systems also is difficult because of their
remote locations.  The aircraft system, which can cover large areas in a
relatively short period, is a practical alternative method, Krabill explained.
Repeated surveys in following years would help detect whether the glaciers have
increased or decreased in volume.

     The principal instrument on the aircraft is Wallops' Airborne
Oceanographic Lidar (AOL).  The AOL measures the time it takes for a laser
pulse to reach the ice and return to the aircraft.  Time variations will occur
because of changes in the terrain and the aircraft's altitude.  Using the GPS,
a Defense Department satellite system that allows aircraft or ships to
precisely determine their locations, researchers will derive the elevations of
the glacier.

     The aircraft, which will be based at Sondrestrom, Greenland, will fly 10
missions over the 3-week period.  Some of the flight paths over central
Greenland will correspond to previous ground surveys.  In addition, a ground
crew from Ohio State University will be measuring the surface elevation along a
60-mile section of the aircraft's flight paths.  The flight path will lie
exactly beneath an orbit track of the recently launched European satellite,
ERS-1, which carries a radar altimeter to measure ice-sheet topography.
Comparison of the satellite measurements to aircraft and surface observations
will provide a check on the accuracy of the ERS-1 measurements.

     If the researchers obtain the desired measurements, a reflight over the
same flight paths may be conducted in 1993, Krabill said.  The program is
conducted under the Earth Science Applications Division of NASA's Office of
Space Science and Applications.
 

Date: 24 Aug 91 03:21:49 GMT
From: [email protected]  (jack hagerty)
Subject: Re: NASA project to measure changes in Greenland's polar glaciers
 
In article <[email protected]>
[email protected] (Peter E. Yee) writes: 

>     Some computer climate models show that increased global
>temperatures would partially melt polar ice sheets and raise sea
>level.  
 
It should be made clear that the rise in sea level is due to the ice
melting off of the land mass, not the polar cap.
 
I get absolutely livid when I hear pseudo science types warn about
"melting the polar cap and flooding the coastlines." Think about it.
The ice in the North Polar cap and the parts of the Antartic ice sheet
that are off the coast are *ALREADY IN THE WATER*. They are already
exerting as much of an effect as they can on sea level. Bouyancy,
remember? If you don't believe me, take a glass of ice water, mark the
water lever then check it again after the ice has melted. 
 
Only ice that is currently on land can have any effect on the level of
the oceans if it melts and most of that (i.e. central Antartica) is 
locked away in a desert.
 
If Earth's temperature were to rise there would definately be a 
corresponding rise in sea level, but it would come from the thermal
expansion of the water, not the melting ice caps.
 
- Jack
 
=============================================================================
||Jack Hagerty, Robotic Midwives, Ltd.        [email protected] (smart mailers)||
||Livermore, CA		       ...!uunet!lll-winken!rml!jack (dumb mailers)||
||(415) 455-1143	   jack%[email protected] (desperate mailers)||
||-------------------------------------------------------------------------||
|| The beatings will continue until morale improves. - The Management      ||
=============================================================================
 

    I think this guy Jack (this should be easy stuff, bouyancy, but I had
    it long ago...) is correct with respect to ice in the water melting,
    but boy is there a lot of ice over the antartica and greenland.  
    
    Also, I'm not sure about the Ross ice shelf.  
    
    FYI, the Ross ice shelf is a large, no huge, piece of ice (the size of
    Hudson Bay?) covering the major bay of antartica.  If I am not
    mistaken, much of this ice rests on the floor of the bay (i.e. it
    really isn't a bay in the normal sence, except it is below sea level
    and it is open to the sea, save for the ice).  Should the attachment of
    the Ross ice shelf to the rest of the antartic ice mass weaken and
    allow the ice shelf to move into the antartic ocean, the results would
    be disastrous, to say the least. 
    
    Admittedly, this is not a likely outcome, unless temperatures rise a
    large amount (several degrees c).
    
    Tony