o Does the background wave field modify wave growth? Are its 
directional characteristics important? 
o Is the directional wave spectrum a sufficiently complete 
descriptor? How important are wave groups, which may give 
rise to non-Gaussian statistics? 
o How good are the models? How efficiently can they assimi- 
late the data? 
o How well can we remotely measure the wave field? How well 
can we measure it from orbital altitude? 
o Can we learn any new physics from the measurements? 
o What is the optimum strategy for global wave monitoring? 
Is is practical? Is its implementation likely to improve 
wave forecasting? 
We do not yet know the answers to these questions, but we are begin- 
ning to accumulate a data base which is offering some major contributions 
toward the solutions. 
III. The SIR-B Extreme Waves Experiment off Chile 
From October 8 to 12, 1984, as part of the SIR-B experiment, simultan- 
eous and coincident measurements of the ocean wave directional energy spec- 
trum were made in a NASA P-3 aircraft flying off the southwest coast of 
Chile. Sea states during the experiment ranged from 1.5 m to 4.5 m, and 
included fresh seas, decaying swells, and both unimodal and bimodal wave 
fields. The two primary aircraft instruments were the Surface Contour Radar 
(SCR; Walsh, 1985) and the Radar Ocean Wave Spectrometer (ROWS; Jackson, 
1985), each of which was independently capable of measuring the directional 
energy spectrum. 
Figure 1 illustrates the geometry of the Chile experiment, and Table I 
summarizes the various means of estimating (or predicting) properties of the 
wave field. The SIR-B was operated through a variety of off-nadir incidence 
angles, from 40? to 18?. Independent spectral estimates also were made with 
the airborne optical laser (AOL) and the "AAFE" altimeter, a nadir-looking 
altimeter yielding estimates of significant wave height. In addition to 
the aircraft and spacecraft estimates, the U.S. Navy's Global Spectral Ocean 
Wave Model (GSOWM), which only recently began operating in the Southern Hem- 
isphere, yielded separate estimates of the directional wave spectrum. 
IV. Experimental Results 
Although a complete set of spectral comparisons is available for each 
of the last four days of the experiment, only one set will be shown here, 
that of October 11, 1984. Preliminary comparisons are also reported in Beal 
et al, 1986a, and more complete comparisons of the entire data set will be 
forthcoming. 
Figure 2 shows the four-way comparison of wave number spectra for each 
of the aforementioned methods. The spectra from the SCR, ROWS, and GSOWM are 
all displayed in relative spectral energy density units of m^. The SAR 
308 
  
spe 
Fou! 
sta! 
reli 
ed : 
bot 
dif 
whi 
agn 
wid 
rot 
thr 
act 
lar 
lar 
Thi 
SAR 
for 
bes 
ROW 
Oce 
con 
the 
the 
Spe 
fal 
10( 
inc 
mos 
alt 
Suc 
tin 
VI. 
Ja 
Ly: 
Sul 
VI 
Be