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c°uld
Plex
feather oceanographic satellite that
°cean
environment is critical. However,
alC°nc* e'enlent of his professional note, e|y the assertion that N-ROSS pro-
a “new dimension” in ASW, needs
q n the September 1987 Proceedings, aPtairi David C. Honhart assessed the ential cost-effectiveness of the Navy R0s°te ®cean Sensing System (Ns , ^) oceanographic satellite, which is tiled to launch in Fall 1991. (See p '^OSS: A New ASW Dimension,” -n '!•) His case for a high-resolution,
ntap the acoustic regimes in a com- ocean environment is well pre- ed. To properly employ our antisub- toarine Warfare (ASW) assets as well as evaluate our adversaries’ tactics, a 0r°ugh and detailed knowledge of the tarn, v'des
3 Cj°Ser look, of f ^"ROSS sensor package consists i^j "Ur instruments: the low-frequency cia^r°Wave radi°meter (LFMR); the spe- alti Sensor microwave imager; a radar oteter; and the scatterometer. The C* N-ROSS sensor for providing atid Sca*e synoptic maps of ocean fronts du ,eddies is the LFMR. The LFMR is a pas *requency (5.2 and 10.4 gigahertz) lUtiIVe receiver that delivers coarse reso- 1 a (25 kilometers spatial and 1.0 to tUre |'e*vin thermal) sea surface tempera- vantUata under some conditions. Its ad- sys(a®e over already on-orbit infrared ■[yli^>n's is its ability to penetrate clouds. Point *n ^ICt’ h;ls been its major selling (for 'n Edition to its lack of resolution and CornParison, the National Oceanic (1^0a ^trnosPheric Administration’s kiloml’Sl infrared sensor delivers 1.1 qlaiITIelcrs spatial and 0.2° Kelvin ther- dr;,,,rLesoluti°n), N-ROSS has two other
^backs;
(thaa!n rate limitation—A light drizzle
the i e’tvvo millimeters per hour) negates LFMR.
► Side-lobe contamination—A predecessor of the LFMR, the 6.6 gigahertz microwave channel on SeaSat, a 1978 Oceanographic Satellite, experienced severe side lobe contamination that rendered the data useless within 600 kilometers of land.1
N-ROSS has a much larger low- frequency microwave antenna so some improvement in reducing side lobe contamination should be expected. Even with a tenfold improvement in side lobe suppression, consider this limitation in concert with the LFMR’s other drawbacks and factor out ASW areas where the LFMR would be useless. A partial list would include: the Mediterranean Sea; the Korea Strait and most of the Sea of Japan; coastal upwelling areas off the U. S. West Coast and in the North Arabian Sea; the Kuroshio Current off Japan and Okinawa; parts of the Gulf Stream;
and most of the Greenland-Iceland- United Kingdom gap.
If N-ROSS is a “new dimension,” what does the old dimension look like? Perhaps the best routine (three times a week) fronts-and-eddies analysis is done by NOAA, using conventional information and infrared sensors on the current series of NOAA polar orbiting and geostationary satellites (Figure 1). To date, no simulation has been done to show that LFMR data will actually improve on current techniques. Most pro-LFMR arguments have been simple handwavings: “If we could only see through clouds, our computers could do so much better,” rather than a systematic evaluation of projected versus current capability.
Even more important, what will the competitive oceanographic satellite environment be in N-ROSS’s projected future? Both the Japanese and Europeans
T°<*ed
'tags / February 1988
97
Lee-Lueng Fu and Benjamin Holt, “SeaSat
JPl-
5 u. S-
itions'
ducing satellite oceanography into fleet opera' As Ocean Service Officer at the Naval OceanograP
Command Center, Guam, he was the first to use
of
Commander, Sixth Fleet.
Figure 2: This SeaSat SAR image shows a warm Gulf Stream eddy— and a ship’s wake. If developed, the SAR could also one day deliver realtime, high-resolution information to the ASW tactical commander.
are planning to orbit earth- and ocean- observing satellites, carrying high resolution visual and infrared imagers as well as synthetic aperture radars (SAR) by the early 1990s. The continuing Soviet “Ocean R” satellite series, first launched in 1983, has “a synthetic aperture side looking radar. Working with a wavelength of 3.2 cm., this device sweeps out a swath 460 KM wide with a resolution of 1.5 KM.”2
As mentioned, the United States first orbited a SAR in 1978 on SeaSat. Figure 2 shows that a SAR can, in fact, detect ocean fronts.3 In this example, a warm core Gulf Stream eddy shows up as a brighter shade. A bright spot with a black trail—a ship and its wake—located just below center of the image provides a sense of scale.
What makes the SAR so attractive to our allies and to the Soviets? In short, SAR images high-resolution ocean fronts and eddies (in tens of meters); is effective in almost all weather (extremely high sea states nullify the sensor); provides information up to and over the beach (SAR is also useful for terrain analysis); images high-resolution ice; and tracks wave period and direction.
If SAR is so superior to the LFMR, why hasn’t it been pushed? The answer is not cost. A SAR could be put on orbit for approximately $10 million less than an LFMR ($60 million versus $70 million) and at substantially less engineering risk. The reason lies in data management. In 1978, it took weeks to process a SAR image and only a limited number of ground stations could copy the signal. Can 1990-95 technology deliver near real-time, high-resolution SAR imagery to the tactical commander? There is a strong probability that it can.
One additional point is worth noting. Surface wind speeds, which are important for ambient noise, sonobuoy washover, and sea keeping calculations can be observed either by the special sensor microwave imager or the scat- terometer. The former was on board the Defense Meteorological Satellite (DMSP F-8) launched in June 1987. The capability to obtain surface wind speed directly from a satellite is on orbit now.
This article’s concentration on the LFMR has been deliberate for several reasons:
► It is the prime sensor for an ocean
fronts-and-eddies analysis.
► It is by far the most expensive of N-ROSS sensors.
► It poses the largest engineering risk (a 5.9-meter rotating antenna).
► Its mission can be fulfilled in a farsU' perior manner by a SAR at a lower cos1
The “new dimension” offered by the proposed N-ROSS sensor package is ne>" ther a new nor a particularly effect've ASW capability. It is not competit've with what the Soviets have had on orb'1 since 1983 and certainly does not the European and Japanese satellite planned for 1990-95. Before subscribe to a $300 million-plus satellite, it is aP' propriate to evaluate critically N-ROSS s ability to help solve the ASW problem'" and the alternatives available, as we*1- lT. S. Allan, editor, “Satellite Microwave
Sensing” (New York: Halsted Press, 1983), P- ' ( 2Nicholas L. Johnson, “The Soviet Year in SPfj 1986,” Teledyne Brown Engineering, 1987. P- 3 - - t Vic*
Ocean and Ice with Synthetic Aperture Radar, Publication 81-120, Pasadena, CA. 1982.
Commander Barry is currently assigned to the 1 Space Command. After graduating from Officer Ca didate School, he served on board the USS Rich 820), USS Norris (DD-859), and with the River Patrol Group in Vietnam. After gradual'.^ from the Naval Postgraduate School with an M■$• , Oceanography, he served as ASW Environmeu Prediction Officer on the staff of CommaiwU Cruiser Destroyer Group Two. While at the A Training Center Pacific, he was instrumental in 'ntr
sat
ellite data in routine ASW oceanographic analys'*( He was recently the Oceanographer on the sta'
Improving Submarine Sonar Displays
By S. M. Luria, Joseph DiVita, and Lieutenant David F. Neri, U. S. Navy
ofle
►How many colors can be used at
►How does the nature of the display an
the operator’s task affect how the disp1 should be colored?
How well do Navy sonar operators detect targets in their displays? We know that at times they do not report them as soon as possible; they may prefer to wait until the signal is stronger and they are more certain about their judgment. But even taking such psychological factors into account, it is clear that their performance falls short of what it might be.
Signal detection theory measures how well cathode ray tube (CRT) operators can detect targets under given conditions in relation to the theoretically ideal performance under those conditions. Human operators fall far short of the theoretical optimal performance. After eliminating the psychological variables, the discrepancy that remains must be a result of the way the visual system works. To improve performance, operators’ tasks must be matched to the ways human sensory systems take in and deal with information.
In the search for ways to improve performance, one long-standing suggestion has been to add color to displays. Indeed, color-coded CRT displays will soon appear on board U. S. submarines. Objects may stand out against a background because of their color or their brightness; a great contrast in brightness generally makes objects more visible than color contrast. When many objects are in the field of view, however, the brightness cue breaks down, and color coding tends
to become more effective. .
While adding color can often n12 . display interpretation easier, the incoff2 use of color can make it harder. The > lowing questions, therefore, must addressed: .fl
► What colors should be used and 1 what way?
time without confusing the viewer: ^
nlay
The best way to color a display ^ pends on the type of display and what operator is trying to determine from Thus, display types must be studied seP‘
98
Proceedings / February