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