What is a Scatterometer? How it works? Importance of Scatterometry Expert Systems

1. What is a Scatterometer?
A scatterometer is a microwave radar sensor used to measure the reflection or scattering effect
produced while scanning the surface of the earth from a satellite.
Description of the Scatterometer and How It Works
The scatterometer is a microwave radar designed specifically to measure ocean near-surface
wind speed and direction. The scatterometer consists of three major parts called subsystems.
They are the Electronics Subsystem (SES), the Antenna Subsystem (SAS), and the Command
and DataSubsystem(CDS).
The Electronics Subsystem is the heart of the scatterometer and it contains a transmitter, receiver
and digital signal processor. It generates and sends high radio frequency (RF) waves to the
antenna. The antenna transmits the signal to the Earth's surface as energy pulses. When the
pulses hit the surface of the ocean it causes a scattering affect referred to as backscatter. A rough
ocean surface returns a stronger signal because the waves reflect more of the radar energy back
toward the scatterometer antenna. A smooth ocean surface returns a weaker signal because less
of the energy is reflected. The echo or backscatter is routed by the antenna to the SES through
waveguides (rectangular metal pipes that guide RF energy waves from one point to another). The
SES then converts the signals into digital form for data processing.
The CDS is essentially a computer housing the software that allows the instrument to operate. It
provides the link between the command center on the ground, the spacecraft and the
scatterometer. It controls the overall operation of the instrument, including the timing of each
transmitted pulse and collects all the information necessary to transform the received echoes into
wind measurements at a specific location on Earth. To locate the precise position on Earth at
which the echo was taken, the CDS collects (for each pulse) the antenna rotational position,
spacecraft time, and an estimate of the spacecraft position. The CDS also collects instrument
temperature, operating voltages and currents, so that the overall health of the instrument can be
monitored. It is through the CDS that the other two subsystems receive the commands that
control all of their functions.
The SAS consists of a one-meter parabolic reflector antenna mounted to a spin activator
assembly, which causes the reflector to rotate at 18 Rpm's (revolutions per minute). The activator
assembly provides very accurate spin control and precise position or pointing information to the
CDS. Optical encoders, glass disks with small patterns printed on the surface, tell the CDS
exactly where the antenna is pointing to about 10/1000 of a degree. The antenna spins at a very
precise rate, and emits two beams about 6 degrees apart, each consisting of a continuous stream

2. of pulses. The two beams are necessary to achieve accurate wind direction measurements. The
pointing of these beams is precisely calibrated before launch so that the echoes may be
accurately located on the ground from space.
Why is Scatterometry Important?
Data derived from ocean scatterometers is vital to scientists in their studies of air-sea interaction
and ocean circulation, and their effects on weather patterns and global climate. These data are
also useful in the study of unusual weather phenomena such as El Niño, the long-term effects of
deforestation on our rain forests, and changes in the sea-ice masses around the Polar Regions.
These all play a central role in regulating global climate.
Computer modeling of global atmospheric dynamics for the purpose of weather forecasting has
become an increasingly important tool to meteorologists. Scatterometer data, with wide swath
coverage, have been shown to significantly improve the forecast accuracy of these models. By
combining scatterometer data of ocean-surface wind speed and direction with measurements
from other scientific instruments, scientists gather information to help us better understand the
mechanisms of global climate change and weather patterns.

3. A knowledge-based system(KBS) is a computer program that reasons and uses a knowledge
base to solve complex problems. The term is broad and refers to many different kinds of systems.
The one common theme that unites all knowledge based systems is an attempt to represent
knowledge explicitly and a reasoning system that allows it to derive new knowledge. Thus, a
knowledge-based system has two distinguishing features: a knowledge base and an inference
engine.
Knowledge-based systems were first developed by artificial intelligence researchers. These early
knowledge-based systems were primarily expert systems – in fact, the term is often used
interchangeably with expert systems, although there is a difference. The difference is in the view
taken to describe the system:
 "expert system" refers to the type of task the system is trying to assist with – to replace or
aid a human expert in a complex task typically viewed as requiring expert knowledge
 "knowledge-based system" refers to the architecture of the system – that it represents
knowledge explicitly, rather than as procedural code.