khayo@sonia.math.ucla.edu (Eric Behr) (06/29/88)
Downloaded from NASA SpaceLink BBS, Huntsville, Ala. (205) 895 0028
====================================================================
6/23/88: NASA SATELLITE TECHNOLOGY AIDS FUTURE SPACE RESEARCH MISSIONS
June 23, 1988
RELEASE: 88-84
NASA's Seasat satellite, launched 10 years ago this week,
ushered in a new era of space research focusing on unsolved
questions of the world's oceans and weather.
Launched on June 26, 1978, on an Atlas-Agena rocket from
Vandenberg Air Force Base, Calif., Seasat carried a payload of
five scientific instruments unlike any package on previous
remote-sensing satellites.
Seasat tested a payload of advanced sensing instruments and
during its 3-1/2-month mission collected oceanographic
information comparable to a century's worth of observations from
a fleet of ships.
Among the experimental instruments Seasat pioneered were a
synthetic aperture radar, which provided highly detailed images
of ocean and land surfaces; a radar scatterometer to measure
near-surface wind speed and direction; a radar altimeter to
measure the height of the ocean surface and waves; and a scanning
multi-channel microwave radiometer to measure surface
temperature, wind speeds and sea ice cover. The satellite also
carried a passive visual and infrared radiometer to provide
supporting data for the other four experiments.
Seasat demonstrated how space sensors could be used in
oceanography -- becoming a baseline for a new generation of
international missions planned that could provide answers to some
of the world's most baffling and threatening weather phenomena.
Examples include an unusual water warming in the eastern
Pacific Ocean in 1982 and 1983. Called El Nino, this phenomena
caused billions of dollars in damage and considerable loss of
life. Scientists also are investigating an increase of carbon
dioxide in the atmosphere, which could have severe consequences
on plants and animal life. Missions derived from Seasat are
expected to help scientists understand both phenomena.
These new generation of oceanographic missions are expected
to provide important, cost-saving aids for such industries as
fishing, shipping and offshore oil production; the National
Oceanic and Atmospheric Administration; and the U.S. Navy.
TOPEX/Poseidon and the NASA Scatterometer (NSCAT) are two
oceanographic missions scheduled.
TOPEX/Poseidon, a joint satellite mission with the French
space agency (CNES), is scheduled for a late 1991 launch on an
Ariane rocket. It will map the circulation of the world's oceans
using a radar altimeter.
NSCAT is a second-generation instrument being developed to
measure wind speed and direction over the oceans' surfaces. A
proposal to fly NSCAT as part of the payload on Japan's planned
Advanced Earth Observation Satellite is currently under
review.
Both TOPEX/Poseidon and NSCAT are intended to support
oceanographic studies during the 1990s under the World Ocean
Circulation Experiment and the Tropical Oceans Global Atmospheres
Experiment. These programs, sponsored by the World Climate
Research Program and scheduled to continue operations for a
decade, involve studies at and below the ocean surface in all
parts of the world's seas.
Other international projects scheduled include the European
Space Agency's first remote-sensing satellite, Earth Resources
Satellite 1 due for launch in 1990; Japan's Earth Resources
Satellite 1 scheduled for a 1992 launch; and Radarsat, a proposed
1994 mission that would be a cooperative venture between Canada
and the United States.
Seasat's technology has not been limited to satellite
oceanography.
The Shuttle Imaging Radar (SIR), a series of synthetic
aperture radar experiments flown on the Shuttle was a direct
follow-on of Seasat's synthetic aperture radar. This marked the
first time NASA had flown that advanced radar instrument in
space.
The first and second experiments in the series, SIR-A, which
flew on a shuttle mission in 1981, and SIR-B, a shuttle payload
in 1984, offered scientists several unexpected discoveries. SIR-A
pierced cloud-covered rain forests of Guatemala to reveal
previously unknown agricultural canals dug by the ancient Maya.
SIR-B penetrated the sands of Egypt to produce a picture of a
riverbed buried for many centuries.
NASA's Jet Proplusion Laboratory (JPL), Pasadena, Calif. is
currently working on SIR-C slated for a 1991 shuttle mission. It
will be combined with a German/Italian X-band radar. Also
planned is an advanced radar system that will be flown on an
Earth Observing System platform as part of NASA's Space Station
program in the late 1990s.
A radar similar to the first flown on Seasat is scheduled on
NASA's Magellan mission to Venus in April 1989. Magellan will use
a synthetic aperture radar to pierce Venus' dense cloud cover to
provide the most complete, highest-resolution images of the
planet's surface ever made.
Another planetary mission benefiting from Seasat is the Mars
Observer, scheduled for launch in 1992. That spacecraft will
orbit the red planet to conduct extensive studies of the Martian
surface with instruments including an altimeter derived from
Seasat.
Seasat was funded by NASA's Office of Space Science and
Applications, Washington, D.C. Gene Giberson was JPL Seasat
project manager; James A. Dunne was project scientist. S.W.
McCandless, Jr. was Seasat program manager at NASA Headquarters,
Washington, D.C.
An international symposium celebrating Seasat's launch
anniversary will be hosted in London next Tuesday through
Thursday (June 28-30) by the British National Space Centre. Gene
Giberson, JPL's project manager for Seasat, and Peter Woiceshyn,
a JPL scientist who has worked on Seasat continuously since its
inception, will be featured speakers.
====================================================================
Ericwooding@daisy.UUCP (Mike Wooding) (06/30/88)
In article <13979@shemp.CS.UCLA.EDU>, khayo@sonia.math.ucla.edu (Eric Behr) writes:
< Downloaded from NASA SpaceLink BBS, Huntsville, Ala. (205) 895 0028
< ====================================================================
...
< NASA's Seasat satellite, launched 10 years ago this week,
< ushered in a new era of space research focusing on unsolved
< questions of the world's oceans and weather.
...
< Among the experimental instruments Seasat pioneered were a
< synthetic aperture radar, which provided highly detailed images
< of ocean and land surfaces; a radar scatterometer to measure
< near-surface wind speed and direction; a radar altimeter to
< measure the height of the ocean surface and waves; and a scanning
< multi-channel microwave radiometer to measure surface
< temperature, wind speeds and sea ice cover. The satellite also
< carried a passive visual and infrared radiometer to provide
< supporting data for the other four experiments.
...
How does the radar altimeter decouple its "height" above ocean
surface from the "height" of the ocean's surface? What scales
are involved (+-10 meters)? A reference point?
< ====================================================================
< Eric
m woodingjwm@stdc.jhuapl.edu (Jim Meritt) (07/01/88)
In article <1313@daisy.UUCP> wooding@daisy.UUCP (Mike Wooding) writes: }In article <13979@shemp.CS.UCLA.EDU>, khayo@sonia.math.ucla.edu (Eric Behr) writes: }< Downloaded from NASA SpaceLink BBS, Huntsville, Ala. (205) 895 0028 }< a radar altimeter to }< measure the height of the ocean surface and waves; } } How does the radar altimeter decouple its "height" above ocean } surface from the "height" of the ocean's surface? What scales } are involved (+-10 meters)? A reference point? There is an altimeter on the geosat that is a follow-up to the seasat one. I do the real-time processing of the data - you not only get "height above ocean", but significant wave height, winds, and a measure of roughness off the altimeter. (probably more, but that is all I lift). This can be used to get current "edges", fronts, eddy locations, and all kinds of neat stuff. I asked about satellite oceanography earlier, but didn't hear about anyone else using altimeter data for oceanography. Anyone else? (geosat is run from here at APL, the only ground station) oh yes - changes in ocean height varies greatly with where on the ocean you get 'em. Biggest off japan..... Disclaimer: Individuals have opinions, organizations have policy. Therefore, these opinions are mine and not any organizations! Q.E.D. jwm@aplvax.jhuapl.edu 128.244.65.5 (James W. Meritt)
eugene@pioneer.arc.nasa.gov.arpa (Eugene N. Miya) (07/07/88)
A U-2 just took off, must be 1100. BTW I saw the Nova on Spy Machines. Thanks for the previous offers. I go on vacation again and some fool at NASA HQ has to send a press release out on a skeleton in a closet [well not that bad]. Let me see if I can address all these notes in a single article [the last time was grossly misinterpreted]. What's this doing in space.shuttle? In article <1003@aplcomm.UUCP> jwm@aplvax.UUCP (Jim Meritt) writes: >In article <1313@daisy.UUCP> wooding@daisy.UUCP (Mike Wooding) writes: >} How does the radar altimeter decouple its "height" above ocean >} surface from the "height" of the ocean's surface? What scales >} are involved (+-10 meters)? A reference point? > >There is an altimeter on the geosat that is a follow-up to the seasat >one. I do the real-time processing of the data - you not only get >"height above ocean", but significant wave height, winds, and a measure >of roughness off the altimeter. (probably more, but that is all I lift). >This can be used to get current "edges", fronts, eddy locations, and all >kinds of neat stuff. I asked about satellite oceanography earlier, but >didn't hear about anyone else using altimeter data for oceanography. This is basically correct. Let me sort out some things. We have questions of scale and decoupling. Now, I didn't work on the Altimeter, (I worked on the SAR) but I had it as a grad school project and talked to most of the people since they were across the street. The Altimeter sent out a 1 ns chirp [square wave]. This gave an inherent resolution of 30 cm (one of GMH's nanoseconds). This made lots of assumptions: 1) the spacecraft was oriented perfectly vertically, the reality was at 800 KM a slight difference in angle is critical. The pulse (chirp) hits the earth in a spherical manner and it radiates it's point of contact. Now the footprint was designed to be 1 KM (if this seems gross, please make an other altimeter suggestion [exer. for reader: why can't use you a laser: answer: won't penetrate clouds]. Anyway, you send out this perfectly spherical chirp (pulse of 1 ns thinkness against a topography of unknown surface roughness, and you get a signal back which is distorted by troughs and peaks of various wave types or land forms. (Like plane cross-sections). Yes, you can get undersea features like canyons and seamounts, but all the instrument does is solve D=cT. The decoupling isn't done using ground stations in realtime, much too expensive and the real-time compute and relativistic effect is murder. Basically I have would have to summarize this book on Accuracy Assessment of Orbit and Height Measurement for Seasat. There are models for satellite orbit which take gravitational anomalies in account, these are plugged into the T data and the sea height and state are "solved." Remember this is all done in nano seconds precision. Also written: >The position of the satellite can be determined in three-space (X, Y >and Z co-ordinates, with no reference to the radius of the Earth), by >the use of radar data from several observers. Studies of the motion This was done infrequently as verification. I have the list of tracking station, but it was not radar, only radio. >derived mathematically from the parameters of the reference geoid, >which was derived from studies of satellite motion in three-space, not >satellite altitude. The expected mean sea level can then be compared >with the actual sea level observed by the radar altimeter, to >determine the variations caused by tides, waves, and meteorologic >phenomena. > >An aside on SeaSat 1 -- The satellite failed some time before the end >of its expected service life. A persistent rumor states that it was >intentionally disabled, possibly by aiming sensors at the Sun; the >purported explanation was that it was able to detect the wakes of >ballistic-missile submarines. > >Kevin Kenny UUCP: {ihnp4,pur-ee,convex}!uiucdcs!kenny Also: >status. I've met one of the engineers in charge of building and >testing Seasat, and he is still bitter about what happened. It was >paul cooper I will be curious, who? Lee @ JPL wrote: >The investigation into the failure of Seasat assigned the probable >cause to a short across the slip rings that transfer the power >generated by the solar cells to the power buss where the solar panels >rotate. They attributed this to the poor design of the slip rings >that had the various voltages (48 rings) alternating plus and minus, >creating the maximun potential to catastrophic electical short. It >was shown that there was a galling problem (in the ring bearings I >believe) that created metal slivers. These slivers more than likely >shorted the main power buss at the rings. The telemetery showed large >voltage and current excursions in the milliseconds prior to loss of >signal from the spacecraft. > >I too have heard unconfirmed rumors of the possibility that SSBM wakes >could be seen in the radar imaging data. I was clear on the images >that I saw that surface wakes were very visible. > >The spacecraft lasted only 90 days in a planned life of one year. I >have had people tell me that they were not unhappy that the spacecraft >had shut down because of the enourmous quantity of data that was >pouring in. We called Seasat-A then -1 after launch (B's and C's were planned as exercises). The "slip ring" on the Agena bus was the cited case of failure by the Congressional Investigative Service. LMSC [Lockheed Sunnyvale] had the burden slapped on them. They had "gotten too lax in the quality control on Agena boosters. You have to understand this satellite was slapped together with parts of an existing booster, not designed from scratch. JPL's scientists were too lax in overseeing LMSC Corp. So said Congress. So how would you lose $90M of the People's money? Regarding FMB subs: shortly before I came on board the project, the Navy Department came by and the SAR group had discussions about resolution, visibility, etc. They didn't want this thing flying at all. Fortunately, other parts of the Navy like the Numerical Weather Central people did want it. Compromises were made. This is the SAR now, not the altimeter. [Oh, SAR== Synthetic Aperature Radar, aka Side-looking Radar, SLAR]. These fears were partially unfounded because the digital processing time for one image was 2 weeks. Partially because it could show where they had been rather than where they were. Optically processed images came out in about a week. Anyway, the project is over, reports are made, a few images were made, SIR [Shuttle Imaging Radar] is off the ground [having a few problems]. Most of the data sits unused. Time for other projects (in this case Magellan). Some reflections, the other day someone stopped me at PARC and noticed an old and faded Project sticker and expressed the conspiracy theory yet again [tired of this]. Launching money into orbit is a sticky thing. One senior engineer (who will go unnamed) was hoping the Atlas was blow up on the pad at VAFB because there were no indication his antenna would unfold in 0-G. I know others who felt the same way about the kludges they had installed and got flight certified. It's like saying, "Your next school project will make or break your future." No second chances. Anyway, we launched at 6:01 PDT. Into the fog, gone in 3 seconds. We went to Solvang for dinner (about 30 miles from where I went to college). Quite a birthday present, three of us (Vickie, myself, and Dave Drake [now at DEC]) -1,0,+2 days). BTW: Dave and I tried getting an early v6 Unix system running on a PDP-11/34 [without MMU]. We learned of Joe Ossanna's satellite tracker [azel] which was not distributed, too bad, we were the space program. Years later, I got "track" from Phil Karn [thanks Phil]. And I occasionally run track with seasat-1 and watch the numbers tick by. It reminds me a bit of the old film Robinson Crusoe on Mars knowing something up there is orbiting because of thing you did. Another gross generalization from --eugene miya, NASA Ames Research Center, eugene@aurora.arc.nasa.gov resident cynic at the Rock of Ages Home for Retired Hackers: "Mailers?! HA!", "If my mail does not reach you, please accept my apology." {uunet,hplabs,ncar,decwrl,allegra,tektronix}!ames!aurora!eugene "Send mail, avoid follow-ups. If enough, I'll summarize." Lee, if you want track, I don't think Phil would object.