OFFSHORE RESOURCE ASSESSMENT - Wind Resource Assessment: A Practical Guide to Developing a Wind Project - page 212

Table 14-1. Satellite-based microwave sensors providing sea-surface wind speed
data

Year of

Satellites Agency launch Instrument Radar band Resolution

Radiometer a SSM/I NASA 1987 K, Q, W 25 km

SAR b

RADARSAR-1 CSA 1995 C ∼ 25 m

SAR b ERS-2/SAR 25 m

TMI NASA-JAXA 1997 Radiometer a X, K, Q, W 25 km
Quick SCAT/Sea Winds NASA 1999 SCAT Ku 25 km
ENVISAT/ASAR ESA 2002 SAR b C ∼ 30 m
AMSR-E JAXA 2002 Radiometer a C, X, K, Q, W 25 km
WindSat NASA 2003 Radiometer a K, Q 25 km
ASCAT/METOP-1 ESA 2006 SCAT C 25 km
ALOS JAXA 2006 SAR b L ∼ 25 m
RADARSAT-2 CSA 2007 SAR b C ∼ 25 m
Abbreviations: CSA, Canadian Space Agency; ESA, European Space Agency; JAXA, Japan Aerospace
Exploration Agency.
a Passive microwave radiometers usually record the earth surface emissivity at several different frequencies.
b Space-borne SARs have different beam modes, each with different pixel sizes.
Source : Beaucage et al., 2008 (7).

ESA 1995 C ∼

Scatterometers. A microwave SCAT is a type of radar. It consists of a transmit-
ter, which emits microwave pulses toward the earth's surface, and a receiver, which
receives their echoes. (In most SCATs, the transmitter and receiver employ the same
antenna.) An empirical relationship relates the backscattered signals to the wind speed
at 10 m height. Rainfall can contaminate the signals from SCATs, especially those that
operate at smaller wavelengths (higher frequencies), but a rain flag provided with the
data allows the analyst to remove such contamination. The leading SCATs cover more
than 90% of the ocean surface on a daily basis at a resolution of about 25 km. Like
passive microwave radiometers, their coverage and quality are limited near shore-
lines. Unlike radiometers, however, SCATs can also measure the wind direction, an
important advantage for resource assessment.

Synthetic Aperture Radars (SARs). While SCATs were designed expressly to
map global ocean winds, SAR systems were built for a variety of research purposes,
such as ice characterization and mapping, oil spill detection, ship detection, and wind
and wave measurements (8). SARs analyze the same characteristics of the backscatter
signal as do SCATs, but they can achieve much finer spatial resolution (as high as
10 m) through signal processing tricks that allow the moving transmitter/receiver to
mimic a much larger antenna. Like SCATs, SARs use an empirical relationship to
derive the surface wind speeds from the backscattered signals. In contrast to SCATs,
however, SAR systems cannot measure wind direction directly, although it can some-
times be inferred from the presence of atmospheric roll vortices or wind streaks.
More commonly, the analyst must obtain directional data from another source (such