For more information, refer to The Airman’s
Information Manual, which is the official guide to flight
information and air traffic control (ATC) procedures,
and is used primarily by pilots, naval flight officers, and
air traffic controllers. This publication is promulgated
quarterly by the Federal Aviation Administration and
contains useful information from a pilot’s perspective.
All forecasters should be familiar with this publication.
FORECASTING PROCEDURES
The first step in the forecasting of altimeter settings
is to forecast the sea level pressure for the valid time of
the desired altimeter reading. This may be done by
using the recommended procedures of prognosis
presented in earlier chapters of this training manual.
The next step is modification of the sea level
pressure. After the value for the expected sea level
pressure has been obtained, it is modified to reflect the
diurnal pressure change at the location in question,
Pressure tendency charts, locally prepared diurnal
curves, and other available information may be used to
obtain representative diurnal changes.
The final result of the first two steps will normally
be expressed in hectopascals since it is conventional to
work in these units on related charts. If this is the case,
then the resultant pressure in hectopascals must be
converted into inches of mercury before it can be used
for an altimeter setting.
In the next section, we will consider the use of
electro-optical (EO) systems by the Department of
Defense. Because EO systems are being used more and
more, it becomes important that Aerographers know
about the problems associated with these systems.
FORECASTING ENVIRONMENTAL
EFFECTS ON ELECTRO-OPTICAL
(EO) SYSTEMS
LEARNING OBJECTIVES: Identify how the
environment affects EO systems, and state the
problems associated with these systems,
Explain the lessons learned with EO systems.
EO systems are concerned with millimeter-wave,
IR optical, and UV wavelengths, As these wavelengths
decrease, resolution increases, but at the same time there
is a decrease in penetration and range. Typically, these
systems are line of sight.
BASIC EO PROBLEMS
The following problems should be considered when
dealing with EO systems:
l You must assess the environment’s effect on the
ability of a line of sight instrument to detect or track a
target. The view of the instrument might be obscured
by material in the atmosphere or may be distorted by
refraction.
l There maybe some limited range over which the
EO sensor will work.
. Cloud layers affect some sensors.
l Battle-induced smoke or dust restrict ranges.
. Time-of-day will be a limiting factor, if the
sensor relies on reflected sunlight or distinct contrasts
(visual or thermal).
. Radiative transfer - as electromagnetic energy
travels through the air.
—
—
—
—
—
Some of the energy may go unimpeded,
directly from the source to the detector,
Some energy may be scattered away (loss);
energy not associated with the source may
be scattered toward the sensor (noise).
Some energy may be absorbed before it ever
gets to the sensor (loss).
Some energy may even be emitted from
particles within the path (more noise).
These effects, along with signal loss due to
spherical spreading, all contribute to
attenuation of the desired signal.
. Spreading - The energy going from the target
back to the sensor undergoes further loss due to
spreading. This is true even for the return trip
(reflection) for an active sensor, although the spreading
of the transmitted energy is focused or beamed.
l Contrast - For adequate detection on tracking,
sufficient contrast must exist between the intended
target and its background. Background might be the sea
surface, sky, or terrain. The EO sensor may use thermal,
textural, color, light intensity, or pattern contrasts as the
method for detection. Insufficient contrast between the
intended target and the background causes no
acquisition or tracking. Radiative crossover is a key
example. The temperature between a metallic object
and the ground has different rates of heating and cooling.
10-6
