Broad Spectrum
Aerial Photographic Analysis
of Aircraft Accident Sites
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by SSgt Rob Jensen
E-Mail:
jensen.robert@ccgate.eielson.af.mil
United States Air Force
HAZE REDUCTION
Tiny particles suspended in the air reflect blue light and cause haze. The
infrared film is not sensitive to blue light (560 nm and lower) so most
atmospheric haze is eliminated. When haze obscured accident site features on
routine color aerial photographs, infrared false color prints documented site
details with much better contrast resolution.
SOIL DISRUPTION
Documentation and analysis of soil disruption patterns that reflect ground
impact events is a primary application of broad spectrum aerial photography.
Soil disruption patterns on photographs normal to the initial ground impact area
provide information about aircraft configuration, attitude and flight path angle
at impact. This information is essential to reconstruction of the accident
sequence. Infrared photographs usually improved terrain contrast, promoting soil
disruption pattern recognition. Occasionally soil disruption areas not apparent
on routine color prints were obvious on false color infrared prints. Displaced
subsoil sprayed over undisturbed surface soil stands out in infrared prints
because of variations in moisture content but is not discernible on standard
color prints.
BURN PATTERN
Burn patterns from crash related fires are characterized by black soot on both
normal color and infrared films. Infrared film is more sensitive than
conventional film to variations in soot density which is burn patterns and
variations in soot density, broad spectrum photography aids accident sequence
reconstruction. Asymmetry of burn patterns may correlate with prevailing winds,
aircraft fuel distribution, impact attitude and other factors.
HYDROCARBON TOXICITY
Fuel and other hydrocarbons spilled in vegetated areas quickly produce plant
toxicity patterns not seen on normal color films but easily detectable on false
color infrared photographs. The liquid hydrocarbons including engine oil, fuel,
transmission fluid, and hydraulic fluids decrease infrared reflectance from
contacted plants before surface color changes are detectable. Hydrocarbon
dispersion in conjunction with burn patterns correlate with prevailing winds,
aircraft fuel distribution, impact attitude and other factors in the accident
sequence. In one investigation asymmetry of the fuel spill pattern provided
evidence suggestion a significant fuel imbalance. Wreckage examination confirmed
this impression and the accident investigation board considered fuel imbalance
an important factor in the mishap. In other cases, infrared photography along
the final flight path documented fuel spills secondary to tree strikes and
inflight break-up of the aircraft.
HEAT DAMAGE
Heat injured vegetation usually has decreased infrared reflectance. Even minor
heat damage is easily detectable on infrared photographs. The infrared changes
from heat damage are similar to hydrocarbon toxicity by are more focal. Infrared
photographs from one accident site demonstrate heat damage to conifers from
ejection seat rockets and jet engine exhaust.
WRECKAGE DISTRIBUTION
Wreckage distribution correlates closely with aircraft break-up and the overall
accident sequence. Aerial views of the accident site aid reconstruction of the
accident sequence from wreckage distribution patterns and supplement other data
including aircrew injury patterns. Aerial perspectives are particularly helpful
in accidents with widely scattered wreckage such as inflight break ups and high
speed, low angle ground impacts. The enhanced contrast and haze reduction of
infrared photography helped locate missing aircraft fragments in several
accidents.
TREE STRIKES
Infrared photography is particularly useful for detecting tree strikes. The
inner wood of trees appears brilliant white on infrared photographs so tree
strike patterns are more explicit on infrared false color prints. Infrared color
photographs from several accidents demonstrated small exposed wood surfaces,
such as branch tips, associated with rotor blade and ejection seat tree strikes.
These features were not visible on ordinary color photographs.
SUMMARY
Broad spectrum aerial photography is a useful and practical tool in aircraft
accident investigations. Soil disruption patterns, wreckage distribution, burn
areas and fuel dispersion patterns often appear in greater contrast and detail
in infrared photographs. Analysis of false color infrared photographs may reveal
missing aircraft parts and subtle evidence of tree strikes. Special infrared
properties allow early detection of foliage changes due to hydrocarbon toxicity
and heat damage.
by SSgt Rob Jensen
E-Mail:
jensen.robert@ccgate.eielson.af.mil
United States Air Force
4927 B. N Seward Ave
Eielson AFB AK. 99702
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