NEIC
i
THE USE OF AERIAL RECONNAISSANCE TECHNIQUES
FOR THE MONITORING OF OIL SPILLS ON WATER
Instruction Report
August 1981
x-xEPA
national enforcement investigations center
denver federal center bldg 53, box 25227 denver, co 80225
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Office of Legal Counsel and Enforcement
THE USE OF AERIAL RECONNAISSANCE TECHNIQUES
FOR THE MONITORING OF OIL SPILLS ON WATER
Instruction Report
August 1981
Arthur W. Dybdahl
Environmental Scientist
NATIONAL ENFORCEMENT INVESTIGATIONS CENTER
Denver, Colorado
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DISCLAIMER
Mention of trademark or brand name
does not constitute an endorsement by
the Federal Government.
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INTRODUCTION
BACKGROUND
CONTENTS
1
1
APPLICATION
1
AERIAL PHOTOGRAPHY PROCEDURES
Camera Requirements .
Photography Requirements
Proper Flight Altitudes
Aircraft Requirements
....9
• • . . 11
• • . . 12
1 Oil Slicks on Water, Ultraviolet Aerial Photograph
2 Oil Slick on Water, True Color Aerial Photograph
3 Pair of Multiband Photos
4 Photomosaic Showing Oil Slicks on Water
5 Dampening of Capillary Waves by Oil Slick
TECHNICAL REFERENCES 13
TABLE
1 Aerial Photography Exposure Values . . . . • . . 10
FIGURES
3
4
5
7
S
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THE USE OF AERIAL RECONNAISSANCE TECHNIQUES
FOR THE MONITORING OF OIL SPILLS ON WATER
INTRODUCTION
This training report explains the use of aerial reconnaissance to de-
tect and monitor oil spills and the resultant oil slicks on marine and in-
land waters. Drilling muds that are spilled into the water near the sur-
face and the resultant turbidity clouds dispersing in the water are also
easily detected.
The objective of this report is to explain the use of aerial photog-
raphy in the detection of oil slicks on water and the dumping/spilling of
drilling muds in the near-surface waters and to delineate the procedures to
be employed to conduct the necessary aerial reconnaissance.
BACKGROUND
Aerial reconnaissance (photography) has been used in EPA enforcement
for the detection and semi-quantification of oil slicks on water for over
10 years. This technology has been applied as standard operating procedure
for aerial photography flights over the nation’s inland waterways and ma-
rine waters.
Extensive laboratory and field experimentation was conducted at the
National Enforcement Investigations Center (NEIC) using various photograph-
ic films, optical filters, and film processing techniques to find the best
combinations for this application. The best combinations are described
later in this report.
APPLICATION
The best photographic technique of aerial reconnaissance used in the
detection of oil spills and oil slicks on water has employed the ultra-
violet region of the optical or light spectrum. It is well known that oil
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2
on water, when exposed to ultraviolet light, exhibits optical fluorescence*
in the near ultraviolet and the deep blue regions of the optical spectrum.
This technique has been used successfully for the semi-quantitative measure-
ment of oil and water especially in coastal and inland waters where there
are many optical color interferences due to numerous causes, such as turbi-
dity, chemical waste, etc. Oils on water exhibit fluorescence in sunlight
but solids and most, if not all, common liquid pollutants do not. Figure 1
is an ultraviolet aerial photograph that clearly shows the presence of oil
on water in gray elongated patches from shore to shore. The light gray
area along the upper shore is a very thin oil slick which, in true color
photography, would be recorded as a silver sheen. The darker gray patches
in the center of the channel, left side of the photo, would display a rain-
bow appearance or rendition in true color. Figure 2 is an example of an
oil slick on water (lower center of photo near the dock) recorded by true-
color photography. The presence of the oil on water is not nearly as vivid
in this photo as it is in the ultraviolet photo [ Figure 1]. In both photos,
the rainbow rendition is present.
True color aerial photography can be used to record and monitor the
presence of oil on water if the water is a reasonably constant natural
color. It will not be as effective in recording thin slicks (silver sheen)
as the ultraviolet photography. An example of this is shown in Figure 3.
The top photo is true color and the oil slick is shown along the near
shoreline out into the middle of the channel (left side of photo). (The
bright area along the left edge of the photo in the channel is due to sun
glint, the reflection of sunlight off capillary waves.) The bottom ultra-
violet photo was recorded by another adjacent camera at the same instant as
the top photo. It shows the oil slick more clearly than the true color
photo even though it is about one stop underexposed. The color of the water
* The definition of fluorescence is the emission of or the property of
emitting electromagnetic radiation usually as visible light resulting
from and only during the absorption of radiation from some other
source (oil emits light as a result of having absorbed ultraviolet
radiation from incident sunlight).
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3
Figure 1. Oil Slicks on Water,
Ultraviolet Aerial Photograph
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4
Figure 2. Oil Slick on Water,
True Color Aerial Photograph
U I ’
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5
f
_ t = -I-
i t it
Figure 3. Pair of Multiband Photos
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in the true color photo is nearly even with exception of along the far
shore. The large shadow in the upper center of this photo is due to a
cloud blocking the incident sunlight.
Figure 4 is a photomosaic of a series of four ultraviolet photographs
showing numerous oil slicks along the channel. The source of the oil spill
or discharge is the petroleum refinery at the lower left.
An oil slick on water dampens naturally occurring capillary waves as
is depicted in Figure 5. The gray area in the center of the ultraviolet
photo extending left to the dock is the area of the oil slick. The char-
acteristic gradations in gray levels show, or indicate, that the oil slick
has the rainbow rendition or effect. The light areas in the water are due
to sun glint. This dampening effect does not always indicate the presence
of oil. This is indicated in the dark area extending from the dock toward
the bottom of the photo (left center); this dark area is a convective-cur-
rent or a Langmuir slick. However, in the converse, there are usually no
appreciable amounts of oil in areas where the capillary waves are present.
As a matter of interest, the thickness of an oil slick on water where the
rainbow effect is present ranges from 1 to 10 micrometers, and the thick-
ness of a silver sheen is usually about 0.1 micrometers.
In offshore drilling operations, drilling muds are present and may
potentially be spilled or dumped into the ambient water under or around the
drilling platform. Aerial photography can be easily applied to the detec-
tion of these muds in the surface/near-surface waters. The muds usually
are manifested as turbidity clouds in the water being either yellow-gray,
yellow-brown, or medium brown. In this color band or region of the light
spectrum, true color photography is the best technique for the remote de-
tection of the turbidity cloud. This technique will record the presence of
the suspended sediment at the water’s surface and usually will penetrate
the surface from 1 to as much as 10 meters or more depending upon sunlight
angle (time of day), camera angle (photos not exposed toward the sun), and
seastate (sunglint).
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Figure 4. Photomosaic Showing Ofi
Slicks on Water
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Figure 5.
Dampening of Capillary Waves
by Oil Slick
8
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AERIAL PHOTOGRAPHY PROCEDURES
Camera Requirements
The aerial reconnaissance of oil spills and oil slicks can be easily
conducted with a hand-held camera from a light aircraft.
The best camera to use is one which uses 70 mm film, 2¼ in. x 2¼ in.
format (image size) for each exposed photo (frame). The camera used by
NEIC is the HasseIblad 500 EL with a motor-driven film advance (the Hassel-
blad 500C has a manual film advance). The camera should be equipped with a
150 mm focal-length lens or an 80 mm lens. The 70 mm film provides a for-
mat size that is large enough to interpret directly with moderate ease.*
The image can easily be enlarged and printed for report use, etc.
A 35 mm camera, which has a format of only 24 mm x 36 mm, can be used.
In this case each frame of film would probably have to be enlarged and
printed to obtain useful results. With this type of camera body, one would
need to use a variable focal length lens. NEIC uses a Vivitar Series 1
zoom lens (70 mm - 210 mm).
The camera lenses used for ultraviolet photography do no need to have
specialized quartz lens elements in this particular application.
It is advised to have the aperture and the shutter speed values cali-
brated throughout each entire range for each camera to be used in this ap-
plication. Any camera service shop can usually perform the necessary
calibrations.
Photography Requirements
The proper photographic film, optical filters, and proper exposure
values are given in Table 1. Ultraviolet photography uses a black and
* The film should be viewed on a light table with a photo-interpreter’s
microscope or tube magnifier.
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Table 1
AERIAL PHOTOGRAPHY EXPOSURE VALUES
Type of
Photography
Film
Type
Kodak Film
Designation
ASA
Optical
Filter
Filter
Factor
e
Exposure
Bright
Sunlight
Cloudy
Overcast
g
ultraviolet
8/W (negative)
Plus-X (2402)8
125
Wratten
39 d
3
stops (8)
f/2 8 @ 1/500
f/2
8 @ l/l 25
Best
II
II
It
Wratten
47A
II
II
“
“
Tri-X (2403)8
400
Wratten
39 d
3
stops (8)
f/5 6 @ 1/500
f/2
8 @ 1/500
Best
(I
It
‘
Wratten
47A
It
II
true-color
color slide
Ektachrome 648
64
Wratten
1A
0
f/5 6 @ 1/500
f/2
8 @ 1/500
“
‘
Wratten
2A
0
“
“
Ektachrome 200 b
200
Wratten
1A
C
f/ 11 h 1/500
f/5
6 h 1/BOO
Best
‘
“
“
Wratten
2A
0
•I
‘
Ektachrome 400 b
400
Wratten
1A
C
f/16 @ 1/500
f/8
@ 1/500
Best
“
“
Wratten
2A
0
‘
2448
64
Wratten
1A
C
f/5 6 @ 1/500
f/2
8 @ 1/500
Best
“
“
Wratten
2A
0
“
“
a Film type available in 35 mm and 70 mm sizes
b Film type available in 35 aim only
c Film type available in 70 mm only
d Glass filter, all others are gelatin
e First value is aperture setting, the second Is shutter speed in seconds
f If camera lens is faster than f/2 8, adjust shutter speed toward 1/500 sec accordingly
g Best film and filter combination to be used
h If sky is hazy, increase exposure ½ stop.
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white (B/W) film which is the best technique for photographing oil spills
and oil slicks on water. The true color photography uses Kodak Ektachrome
film (true color transparency or slide). It is recommended that both types
of photography be used for each site to be photographed. The true color
photography will best show the presence of any drilling mud in the surface
and near-surface waters as would be expected in offshore drilling opera-
tions. In this latter case, the use of an optical polarization filter over
the camera lens may help to significantly reduce sea surface reflections,
depending on seastate. If such a filter is used, each true color exposure
value given in Table 1 must be increased two stops with the polarization
filter manually oriented so that the surface reflections are minimized.
This filter cannot be effectively used for ultraviolet photography.
The films given in Table 1 along with the optical filters are standard
and are available through the Kodak Federal Supply Schedule in any regional
procurement office.
The camera’s internal exposure meter (35 mm SLR camera) or an external
light meter cannot be used for ultraviolet photography. The exposure val-
ues in Table 1 should be used to set the camera properly. (The Hasselbiad
camera does not have a built-in exposure meter.) The exposure meter or an
external light meter can be used for true color photography; however, the
exposure values given in Table 1 are highly recommended.
The film should be processed as soon as practical after it has been
exposed. Keep all film refrigerated or, better yet, frozen until ready to
use. Avoid exposing the film to high temperatures such as in a locked-up
car or airplane.
Proper Flight Altitudes
Proper flight altitudes are basically a function of the focal length
of the camera lens and its film format size.
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For example, using a Hasselbiad 70 mm camera with an 80 mm focal
length lens [ the standard times-l (1X) lens for this camera] the flight
altitude above water’s surface (or land) should be in the interval from
1,000 ft to 1,500 ft. The flight path should be in the form of a circle
with the target of interest near the center. Numerous photographs should
be taken of all areas of the target from at least four different directions
(usually the four cardinal coordinates, NSEW). However, photographs taken
with the sun angle toward the cameras will result, at times, in a large
amount of water reflection or sun glint, rendering them nearly useless.
The photographer can easily minimize this occurrence by visualizing the
target scene through the camera viewer before exposing film.
A Hasseiblad camera with a 150 mm lens (2X for this camera) should be
used in a flight altitude interval from about 2,000 ft to 3,000 ft above
water (ground) level.
A 35 mm camera equipped with a Vivitar Series 1 zoom lens should be
used at an altitude interval of 1,000 to 1,500 ft for focal lengths ranging
from 70 to 105 mm, 1,500 to 2,000 ft for the range from 105 to 150 mm, and
2,000 to 3,000 ft for the range from 150 to 210 mm. When operating this
lens in the range from 150 to 210 mm focal length, the exposure values
given in Table 1 should be increased one-half stop to compensate for the
smaller lens light acceptance angle.
Aircraft Requirements
Nearly any light aircraft (single or twin engine) or helicopter can be
used effectively for aerial reconnaissance. Care must be taken to ensure
that any aircraft that will be flown out over the ocean waters away from
the coast for more than 15 nautical miles has adequate navigational instru-
mentation, especially on cloudy days. Light aircraft, and usually heli-
copters, can be chartered at nearly any FAA-controlled airport in the
country. Another consideration is riding along on the Coast Guard’s rou-
tine patrol flights.
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The photographer must position him/herself within the aircraft near a
window that is free from structural obstructions such as wing struts, etc.
The window may be closed for true-color photography. For ultraviolet pho-
tography, the window may have to be opened, especially if the window mater-
ial has a color cast of any kind, i e. , gray, smoke, pink, yellow, etc.
The photographer must make sure that the window is clean and free from
large scratches, pits, etc.
TECHNICAL REFERENCES
Kodak Publication M-29, Kodak Data for Aerial Photography.
Kodak Publication M-61, Kodak Aerial Films and Photographic Plates.
Kodak Publication B-3, Kodak Filters for Scientific and Technical Uses.
Kodak Publication M-27, Ultraviolet and Fluorescence Photography.
Kodak Publication M-2, Using Photography to Preserve Evidence.
Manual of Remote Sensing, American Society of Photogrammetry, Vols 1 and 2.
Remote Sensing, Optics and Optical Systems, Philip Slater, Addison-Wesley
Publishing Co.
Remote Sensing and Image Interpretation, Thomas M. Lillesand, Ralph W.
Kiefer, John Wiley and Sons.
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