NASA Plans Studies of Global Gravity Field and Forests
3/19/97
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Headline: NASA Plans Studies of Global Gravity Field and Forests
Source: The New York Times Company
Date: 3/19/97
Author: Warren E. Leary
Copyright 1997: The New York Times Company
WASHINGTON -- The space agency announced Tuesday
that it would sponsor two low-cost satellite
projects to study the distribution of the Earth's
forests and to provide a detailed map of the planet's
gravity field.
NASA officials said the new economical projects, part
of the agency's Mission to Planet Earth program, were
intended to complement more expensive space missions to
study the planet's environment.
William Townsend, the NASA official in charge of the
program, said the new missions were part of the
agency's renewed focus on quickly developing and flying
smaller, less expensive spacecraft that have limited
objectives rather than concentrating on billion-dollar
missions that can take decades to plan and launch.
Townsend said a previously planned Earth observing
system that would have used two giant satellites --
each would have carried 15 instruments -- had been
replaced by a dozen or more missions on medium- to
small-sized spacecraft. This system could respond more
easily to changing science priorities, he said Tuesday
after a briefing.
After a competition, NASA selected two of 12
semifinalist projects to finance and a third project to
be sponsored as a backup, in case one of the winners is
canceled for not meeting its scientific objectives,
going over budget or off schedule.
"These exciting missions will deliver their first
science results in a little over three years,
remarkably fast for such capable spacecraft," Townsend
said.
The first to fly is expected to be the Vegetation
Canopy Lidar mission, a satellite that would orbit 250
miles above the Earth, firing energy pulses from five
lasers to the ground.
The mission, the first of its kind, would spend two
years accumulating three-dimensional details of 98
percent of the world's forests and how they are
changing. The satellite is scheduled for launch in
January 2000 on a Pegasus rocket, said Dr. Ralph
Dubayah of the University of Maryland, the chief
scientist on the mission.
Dubayah said the safe, low-power laser beams would scan
strips of forests more than 80 feet wide to determine
the height of foliage, from the treetops to the ground.
That would allow more precise measurements of tree
heights, catalogue information about forest canopy
structure and greatly improve estimates of global
biomass, or the number or mass of living organisms in a
particular area, he said.
The laser pulses, which would bounce back to the
satellite, would also allow precise study of the stages
of seasonal changes in forests, such as those that
occur from winter to spring, he said.
The forest survey mission has a budget of $59.8
million, which includes the price of launches, as well
as data gathering and analysis, NASA said.
The second mission selected is the Gravity Recovery and
Climate Experiment, which plans to use two satellites
to be launched by a Russian rocket in 2001, to measure
gravity fluctuations while flying in formation 280
miles above the Earth.
A team headed by Dr. Byron D. Tapley of the University
of Texas in Austin plans to work with a German group
led by Dr. Christoph Reigher of GeoForschungsZentrum in
Potsdam, Germany, to launch and operate the satellites
for up to five years.
NASA plans to spend $85.9 million on this mission for
the U.S. investigators to build the satellites and
instruments. The Germans agreed to contribute an
additional $40 million to buy a Russian Cosmos
launching rocket and to control mission operations,
officials said.
The satellites, expected to fly 60 to 250 miles apart
in the same orbit around the Earth's poles, would be
linked by microwave signals to calibrate their distance
from each other and changes in movement caused by the
gravitational pull of large metal deposits on Earth.
Tapley said these changes would pinpoint permanent and
changing features on Earth that affect gravity, and
also could be used to locate and map resources like
aquifers, or underground reservoirs of water.
If one of these missions was canceled, NASA said it
would invest up to $500,000 over two years for
preliminary work on a backup project to map the
movement of 30 types of gases, particles and pollutants
in the atmosphere.
The project, headed by Michael Prather of the
University of California at Irvine, would cost a total
of $87.5 million over about three years and involve
launching a satellite in 2001 that would collect light
passing through the earth's atmosphere at sunrise and
sunset to measure pollutants.