obscuration is related to word "obscure" =block/shroud/mask/conceal/veil/ hide, http://www.thefreedictionary.com/obscurations

https://en.wiktionary.org/wiki/obscuration
it's also a unit of measurement used in particular for smoke detectors which respond to absorption of light by smoke, in percent absorption per unit length, e.g. % obs/ft, % obs/m.

https://en.wikipedia.org/wiki/Smoke_detector
Obscuration is a unit of measurement that has become the standard way of specifying smoke detector sensitivity. Obscuration is the effect that smoke has on reducing sensor visibility, expressed in percent obscuration per unit length;[30] higher concentrations of smoke result in higher obscuration levels.
Typical smoke detector obscuration ratings
Detector type Obscuration
Ionization 2.6–5.0% obs/m (0.8–1.5% obs/ft)[27]
Photoelectric 0.70–13.0% obs/m (0.2–4.0% obs/ft)[27]
Aspirating 0.005–20.5% obs/m (0.0015–6.25% obs/ft)[27]
Laser 0.06–6.41% obs/m (0.02–2.0% obs/ft)[39]


obscuration is basically related to a darkness/dimness where light from the sun is blocked, for example, because of atmospheric dust/cloud/smoke etc. or where visibility is curtailed in some way. Obscuration can be caused by volcanic activity and non-nuclear explosions as well

[PDF]A Battlefield Obscuration Model (Smoke & Dust) - Defense Technical ...
www.dtic.mil/dtic/tr/fulltext/u2/a080459.pdf
obscurants that may be generated by military activity. These include smoke and obscuring aerosol munitions, dust clouds generated by non-nuclear explosive ...

https://www.science.gov/topicpages/l/large scale obscuration...
Large scale obscuration and related climate effects of nuclear detonations first became a matter of concern in connection with the so-called ``Nuclear Winter Controversy`` in the early 1980s. Since then, the world has changed. Nevertheless, concern remains about the atmospheric effects of nuclear detonations, but the source of concern has shifted. Now it focuses less on global, and more on regional effects and their resulting impacts on the performance of electro-optical and other defense-related systems..."


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Note added at 19 hrs (2017-08-22 12:48:05 GMT)
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There are lots of examples of the word in use but most are Pdf documents which take a lot of time to go through. In a military setting a dust cloud can be formed simply by having a helicopter hover close to ground but there are other "obscurants" as well
http://www.wood.army.mil/chmdsd/images/pdfs/Summer 09/Doctri...
Field Behavior of NBC Agents (Including Smoke and Incendiaries)
3 Nov 86 An MTTP manual which addresses the battlefield influences of weather
and terrain and the use of smoke and obscurants on CBRN operations.


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Note added at 3 days19 hrs (2017-08-25 12:58:36 GMT)
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MASOUD
I ws busy with my own work so just getting back to this now. As I said at the beginning, obscuration means affecting visibility in some way. This can range from trying to hide troop movements, masking plane/tank etc. infrared so they cannot be targetted by enemy missiles or even hiding military installations or airfields/weapons dumps etc. So an army unit in charge of obscuration is going to perform obscuration (masking/hiding tactics) for their own side but also analyse the obsuration tactics of the other side. They will also use weather/terrain data etc. to see how these impact on onscuration or on dispersal/effect of obscurant agents. I've picked out bits from these links
http://www.globalsecurity.org/military/library/policy/army/f...
Chap 7 explains VISUAL-INFRARED OBSCURANT GENERATOR SYSTEMS

Thsi one explains US army operation of obscuration platoons https://www.scribd.com/document/115212794/ATTP-3-11-36-2010
For example, thermometer readings are used to estimate the effect of temperature on (chem/bio etc.) agent duration; data regarding wind speed and direction is used for hazard and obscuration prediction; and information about atmospheric conditions (humidity, air stability) is useful to predict their influence on the use of obscurants.
Consider using obscurants to protect infrared systems

Coordinate with the fire support officer on obscurant missions to cover potential obscuration targets identified during the war-gaming process (suspected enemy observation points, river-crossing operations, deception operations)
The intelligence section provides information on enemy vulnerability to friendly operations (OBS)
Operations: CBRN staff provides recommendations on CBRN reconnaissance,decontamination, and OBS unit employment.
weather considerations Data regarding wind speed and direction for hazard and OBS prediction.
PAGE 154 The USA Chemical Corps maintains two variants of the CBRN obscuration platoon in the modular force design. The primary difference lies with the mobility platform—one variant is mechanized, and the other variant is wheeled…. Obscuration platoons provide large-area obscuration to protect the supported force and enable movement and manoever.
CBRN obscuration platoons typically provide temporary obscuration for single, short-term missions. They may also provide sustained obscuration by integrating on-line fog oil resupply into the operation. Obscurants include visual or infrared-defeating obscuration or a combination of the two.
Mechanized obscuration platoons operate primarily in support of brigade combat teams due to their greater survivability and rough-terain mobility capability. Wheeled obscuration platoons operate primarily in support of division…
P155 Mission: Provides battlefield obscuration to protect tactical-level combat forces across full spectrum operations.
Key tasks: Performs sustained/temporary obscuration operations..
Capabilities: Provides visual obscuration for up to 5sq KM Provides infrared obscuration Is 100% mobile. Is capable of defeating Level II threats….
Employment: Is organic to CBRN company obscuration (mechanized). Operates independently in support of…
Provides protection measures in support of units conducting movement and manoeuver
P158 The U.S. Army maintains its large-area obscuration platoon force by pooling into company formations and pooling allows massing the protection effects on a large scale or task-organizing platoon-size obscuration units to support comat formations, provide obscuration support to the other Services, or operate in support of other missions (protection of key C2, sustainment functions [fog oil resupply, vehicle maintenance, vehicle recovery]). ..battlefield obscuration.)
P161 The third squad in the obscuration platoon is dual-designated as a support decontamination squad, with one heavy decontamination apparatus.

https://www.google.com/patents/US7624666 Example of Infrared obscuration of an aircraft (Note this is civilian aircraft but simple explanation) "The obscuring agent comprises carbon dioxide gas, or water vapor, or a mixture thereof. The obscuring agent is ejected from a dispensing location on the aircraft so as to flow between the hot region and the external viewing location. The obscuring agent has a temperature of less than that of the hot region. In a typical case, the obscuring agent is ejected at a temperature of less than 150° C., so that it does not itself serve as a significant infrared emitter..."