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Visual Lightning Strikes
Measurements of meteorological parameters such as stability irradiance, small-scale features in the wind, vertical temperature gradients, etc., are not done by standard meteorological procedures such as those used by the National Weather Service. Nor does the National Weather Service make measurements of more common meteorological parameters for non-standard locations, times, and sampling periods. Army test-range meteorology groups have the special instrumentation and expertise required to integrate these into test planning at Army test ranges.
Measurements of common meteorological parameters such as temperature, humidity, pressure, wind, ceiling, and visibility for hourly intervals from 12 to 24 hours per day are made by the National Weather Service at locations approximately 100 miles or more distant from each other. Upper-air data from widely separated locations (approximately 200-400 miles) are gathered twice each day. These data are available through the National Climatic Data Center in Asheville, NC. (see also Climatic Data Sources). The National Weather Service (NWS) under the Department of Commerce was organized to support widespread needs of the public, primarily in the area of transportation. It makes and gathers standard meteorological measurements at the surface and aloft on the large-scale, exchanges these data with foreign countries, and runs global and hemispheric scale forecast models at its super-computing center at Silver Spring, MD. Weather news agencies such as the Weather Channel utilize NWS data and forecasts to generate graphical formats to distribute to the public. They are required to monitor severe weather forecasts as they are issued by the appropriate NWS centers, such as the National Hurricane Center in Miami, FL. The Department of Defense has created its own meteorological services for the same reason it has its own aircraft and communications networks: the military mission demands it. Military operations and testing increasingly require meteorological measurements and forecast, on scales much smaller than that available from NWS and public weather news sources. The military also requires data on non-standard measurements requiring instrumentation not possessed by NWS and private meteorological services. These military meteorological activities do not duplicate the civilian services: the two work together synergistically. Military meteorologists including those at ATC depend upon output of the NWS for building specialized products and provide daily feedback to NWS on measurements useful for the NWS computer models. The dipole water molecule interferes with propagation at many places in the electro-magnetic spectrum. So strong is this interference in the 3-10 cm band (discovered in World War II) that radar has become a valuable tool for meteorologists tracking all three phases of water in the atmosphere, liquid water being more disruptive than solid ice. In the millimeter band ice becomes relatively more of a problem than water.
Fog Cloud Smart sensors must be tested in various water environments...ice, snow, rain, fog. These tests ought to include measurements of target-to-background contrasts as well as ground clutter variations. ATC has specialized instrumentation to measure parameters like rainrate and transmissivity. Not doing so will produce unreliable items for the soldier in the field.
It has been reported that mine detection equipment performed poorly in Bosnia under conditions of snow cover that had partially melted and refrozen. Ice crystals may have interfered with the detection technology. Since snow can be exceedingly complex in structure, testing must be done under the proper meteorological conditions to anticipate field performance of smart sensing systems. ATC is optimally suited for four-season, temperate climate testing.
Within the continental U.S., the National Weather Service and the Department of Defense have combined resources to install, maintain, and operate a weather Doppler radar network called NEXRAD. The 10 cm radar itself is called the WSR88D model. For testers NEXRAD can provide a variety of products not previously available. With a spatial resolution of 1 x 1 km square-land surface and temporal resolution of less than 10 minutes, the WSR88D can provide small-scale precipitation and wind structures. Weather-sensitive tests can work around adverse weather in ways never before possible. Infrared and millimeter-wave tests can have precipitation over the test area quantitatively measured. Mortar and indirect fire ballistic tests can schedule costly weather balloon flights economically without missing wind vector changes aloft. ATC has a Principle User Processor workstation tied to the nearest NEXRAD at Dover AFB, DE. Through this workstation ATC meteorologists can receive a large selection of measurements unavailable from public radar displays.
The local climate has a profound effect on the physical environment...vegetation, trees, and soil type. Tests involving target-to-background contrasts, for example, must be done in environments that closely approximate real-life potential conflict areas. Fuzed rounds that must penetrate deep layers of foliage must be physically tested against actual foliage. ATC offers a complete four-season type of foliage background. It also offers a variety of soil types due to its proximity to the Chesapeake Bay. Merely going to a cooler, higher plateau in an otherwise arid region does not equate to testing in temperate climate conditions.
Radio, like radar, is affected by atmospheric conditions. Vertical profiles of temperature and humidity affect the electronic index of refraction. For example, when drier and warmer air overlies moist, cool air, radio propagation from distant transmitters is refracted into receivers normally out of range. Such receivers, if powered for short-range transmissions, can become useless under these conditions. Special upper-air measurements can be taken at ATC to correlate with radio performance. This atmospheric effect also degrades GPS systems in the same manner.
Liquid water droplets in the air disrupt electro-optical transmissions. In infrared systems, rain cools objects differently in the imagery. To make test results truly portable from one site to a potential engagement site, rainrates and amounts should be measured during testing. Virtual Proving Ground modeling requires these measurements for different precipitation scenarios (stratiform vs. convective rains). ATC is uniquely located to receive both kinds of precipitation throughout its four-season year. ATC Meteorology personnel can not only measure rainrates and forecast them, they can also make the non-standard droplet spectra measurement.
Smoke dispersion is of concern not only in chemical smokescreen testing, but also in more ordinary testing that involves smokes as a by-product of the test itself. Environmental air pollution restrictions can severely delay tests and drive up costs. At ATC we protect against such delays with non-standard measurements of the lower atmosphere, and with smoke dispersion modeling.
Sound propagation is shaped by the atmosphere like a lens shapes light rays. The "bending" of sound rays occurs because of changes in the speed of sound. The speed of sound is a function of an air-density parameter called virtual temperature and is also affected by the wind vector. If the speed of sound in a certain direction, for example, increases with height, any loud noise is "focused" toward a surface area distant from the sound source.
Sound Propagation Model Output Sound propagation, therefore, in the real atmosphere is constantly changing, much like the stars "twinkle" (scintillate) at night. Upper-air measurements are needed to characterize such propagation. At ATC we use a time-tested model to determine where sound focusing might occur off-post, before testing with large explosive charges. ATC can also do small-scale measurements close by, with systems that utilize acoustic tracking, and support such testing with specialized forecasts based upon years of experience working in the field.
More often than not, Test Operational Procedures only lay out bare minimums for meteorological parameter measurement. To do a quality test in the most inexpensive manner requires some interpretation of how to collect data that counts.. We urge you to contact ATC meteorologists as early as possible to filter out unnecessary costs in your budget in two ways: (1) by having us show you how to remove unnecessary and incorrect meteorological measurement methods; and (2) by having us suggest meteorological parameters that should be measured during the test that will likely be called for by analysts, after the test . Meteorological principles are not well understood outside of the meteorological community. The most common mistakes of test plans are to use a too-small sample period and to measure at the wrong location. 1. Errors in sample period. Meteorological parameters vary in frequency, and the physics of higher frequency variations is often quite complicated. Too-small sampling periods, are "noisy", and can ruin mathematical models. Sample periods of less than one minute generally are wrong for most tests. Sometimes sampling periods of a much longer duration is needed. Test Operating Procedures will not often give guidance here. 2. Errors in measurement location. Point measurements at a distance from the test article or over terrain varying from that near the test article are largely useless. What relationship, for example, would a one-second wind vector 500 meters away from the test article have with a one-second wind vector at the test article? None!
Atmospheric stability is a measure of the prevalence of horizontal laminar air flow. It is disturbed either mechanically (e.g., wind around obstacles) or thermodynamically (e.g., heat-caused buoyancy). Stability determines length of required sampling period for atmospheric measurements as well as dissipation of smoke, stability of electro-optical imagery, and efficiency of sound propagation. At ATC, atmospheric stability is regularly inferred by a variety or surface and upper-air measurements.
The various standard atmospheres used in the U.S. and elsewhere are attempts at characterizing a mean atmosphere for certain latitude bands on earth. Many tests articles will include in their operational procedures, instructions to input departures-from-standard atmospheric conditions. Such departures require measurements of the same parameters used to define the reference standard. They also require that the measurements be for a sample period suitable to the operation of the test article. "Instantaneous" measurements are not usually the kind required. Consult with ATC meteorological personnel for help, if needed.
Surface meteorological measurements include all measurements made within 10 meters of the ground surface. This zone is considered surface boundary layer in many applications. ATC meteorological capabilities include a sensor-rich network that takes standard measurements.
In one of the most unexpected ways, weather effects can cause target mislocation. Whenever the electro-optical ray from the target to gunsight doesn't follow a straight line, targets will be mislocated. Typically such refraction phenomena occur wherever there are very strong vertical temperature gradients. Note that the cause is temperature gradient, not temperature extremes. Since such gradients occur near the ground, target mislocation due to refraction nearly always involves surface targets. In hot deserts refraction is expected; in less extreme locations it is not. Nevertheless refraction has proven to be a problem in temperate and other non-desert climates. In Alaska, for example, two military units shot TOW missiles at targets. One group missed, the other group scored hits. The difference was that the first group failed to consult meteorological personnel on site about vertical temperature gradients near the ground. The second group did. At ATC, it has been shown, under certain conditions, that refraction will cause a vertical surface target mislocation of six feet or more at 3,000 meters! ATC meteorology personnel can measure the details or surface temperature gradients as well as forecast their general characteristics.
Targets can be obscured in the visible, in the infrared, in the millimeter-wave, or in any combination of these spectral regions. For multi-sensor systems, testing should be rigorously designed to measure obscuration effects in all such combinations. Such testing requires special forecast support to anticipate atmospheric stability conditions for smoke dispersion as well as rainrate and visual range values.
For a mere $400 or less in forecast personnel salaries, savings in test budgets can easily reach $10,000. For tests involving specific types of weather, specialized forecasts are mandatory. ATC offers very helpful, cost-savings forecast support for the long-range, medium-range, and short-range. Test directors save significant funds by using these services. New tests have recently come to ATC, our available weather support being the prime reason. Call us for guidance.
Forgive us for being dogmatic, but test plans that omit weather effects on the article are an invitation to wastefulness at best and to unnecessary battlefield risk at worst. A look at the lessons that have had to be relearned time and time again in history will prove the point. Articles must be tested for weather degradation for the battlefield soldier.
How efficient is the atmosphere in transmitting energy in a given spectral band of the electro-optical spectrum along a path from the transmitter to the receiver? That is the question transmissivity answers. Transmissivity measurement is a non-standard measurement and involves considerable planning and analysis to gather. Questions of relative versus absolute measurement must be answered, as well as which frequency bands should be sampled. Often computer models are used, such as LOWTRAN and MODTRAN, which require more standard meteorological measurements but which suffer the typical vulnerabilities of model assumptions.
Tests involving indirect fire projects, vertical firing for fuze tests, and various special sensor tests all require measurement of temperature, humidity, pressure, and wind in the vertical. Today's technologies provide a variety of methods besides the tried-and-true method of weather balloon launches. At ATC we have data from the lower boundary layer available every 15 minutes through our SODARS, and most of the time data from upper levels every 15 minutes through our NEXRAD WSR88D workstation. Check with us for proper combination for your test.
An oft-forgotten aspect to testing electro-optical sensors is the matter of target-to-background contrast. The visual background environment is largely determined by climate. ATC offers a true four-season background environment along with its excellent test facilities. These visual environments are typical of higher-probability engagement areas of the world.
Wind-chill temperature is a "fake" temperature artificially created as an indicator of heat loss from the human body. It is the temperature that would cause the same heat loss if the wind were 4.5 mph. Higher winds cause more heat loss due to more efficient conduction. For an equivalent heat loss at 4.5 mph, the air temperature would have to be lower than it is in a higher wind speed condition. Thus wind-chill temperature at wind speeds of say, 15 mph, can be below zero (F) when the actual air temperature is in the low 20s. ATC regularly monitors and makes wind-chill temperatures available throughout the winter months. Obviously, an easy strategy to cope with low wind-chill temperatures is to slow down wind speeds near the body either with wind barriers or with "wind-tight" clothing. Another strategy is to avoid outside work, not necessarily at very low temperatures, but at low temperatures with high wind speeds.
Good wind measurements are often difficult to obtain, especially in complex terrain. To get useful wind data for your test, please consult with meteorology personnel. The measurement strategy will depend upon the use you or your customer plan to make of the data. For ballistic testing some thoughtful planning is required. When data is to be taken some distance from the test article, the sampling period needs to be carefully computed. In complex terrain a field survey ought to be done to see if useful measurements are even possible. ATC meteorology personnel are continually experimenting with ways of getting tests good wind data in difficult locations.
ATC meteorological personnel collectively have over one hundred years of experience in the very specialized field of small-scale meteorological measurements and forecasting. Our folks have formal specialized training in SODAR-derived, boundary-level data interpretation, NEXRAD data interpretation, operation of a sizeable meso-meteorological data collection network, military weather forecasting, and military material acquisition, as well as in the electronic repair, system development, calibration and maintenance of the specialized equipment required to perform these service areas. Moreover, they also have years of experience in applied military meteorology both in testing and in war-fighting areas. Most are experienced veterans from the Army, Air Force, and Navy.
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