WESLEY JAMES

PROF. FRED J. BURGESS

Oregon State University

Corvallis, Oregon 97331

Ocean Outfall DispersionAerial photography offers a possible method for evaluating waste concentra­

tions, dispersion processes, and current patterns.

INTRODUCTION

O CEAN OUTFALLS ARE in general located onthe relatively shallow coastal shelf. Be­

cause of heavy seas, sampling from a boat inthis near-shore area is dangerous at all timesand impossible much of the time. A moreeffective and less dangerous sampling tech­nique is desirable. The use of aerial photog­raphy presents a possible method of over­coming this difficulty. Sampling from a boatto define adequately the waste field for evena small outfall requires from two to eight

water will generally rise to the surface. Afterthe initial dilution in the vicinity of the jetdiffuser, the natural turbulence in the oceancontinues to mix and spread the waste.

The use of a dye tracer has been the con­ventional method for studying the dispersionof the waste field from an ou tfall. I n this pro­cedure the tracer is metered into the pipelineon shore. The concen tration in the waste fieldis determined by sampling from a boat andmeasuring the concentration of the tracer. Ifthe flow rates of both the effluent and tracer

ABSTRACT: Aerial photography may provide a method of analyzing dispersionof wastes that are discharged into the ocean. A procedure for determining wasteconcentrations from aerial photography is described. This technique may yieldmore comprehensive results than conventional boat sampling in dispersionstudies. Discrepancies between boat concentrations and photo concentrationsappear to be due primarily to the changing and shifting of the waste in thisdynamic environment. The photographic technique is a method of study thatmay provide information on diffusion which has been impossible to measure byconventional sampling methods.

hours of continuous sampling. Under usualconditions the waste field is continuouslychanging during this period of time, thusmaking a comprehensive study of the disper­sion by conventional means nearly impos­sible. This paper attempts to establish aquantitative aerial photographic technique tomeasure concentrations throughout the wastefield which may be recorded as image densitiesat one instant, thus overcoming many diffi­culties.

An ocean outfall is a pipeline used for diE­charging waste into the ocean and it usuallyterminates with a diffuser section. Here theflow is divided into a number of small jetswhich discharge into the ambient fluid. If anou tfall is located on the coastal shelf in rela­tively shallow water, usually little densitystratification occurs in the receiving body ofwater. The effluent being less dense than sea

are known, the waste concentration can bedetermined from these samples.

RATIONALE

Photographic films used in aerial photog­raphy are sensitive to visible or near-visiblelight. The film density depends on the irra­diance reaching the film. The predominantsource of this energy is the sun. Solar radia­tion passing through the atmosphere is re­duced by scattering and absorption. Theattenuation depends not only on the turbidityin the atmosphere but also on the length ofthe path through the atmosphere. The zenithangle i of the sun is involved in reducing theillumination in two ways. First, the intensityon a horizontal surface is cos i times the in­tensity on a normal plane and, secondly, thepath traversed by the radiation through theatmosphere increases with the secant of the

1241

1242 PHOTOGRAMMETRIC ENGINEERING

FIG. 1. Light from the sea.

angle. The irradiance H. on a horizontalplane at the sea surface can be expressed as

Fl, = Ifo cos i exp (-A sec i)

where H o is the incoming radiation at theouter atmosphere and A is the extinction op­tical thickness for a standard atmosphere andincludes Rayleigh attenuation, aerosol atten­uation and ozone absorption.'

The light reaching the water surface iseither reflected from or refracted through theair-sea interface. If i is the angle of incidenceand j is the angle of refraction, then (sin ijsin j) is equal to the index of refraction forwater, or about 1.33. The reflectivity of thewater surface is theoretically obtained forunpolarized light from Fresnel's law2 whichgives the ratio Pa of reflected energy R toincoming radiation H•. As shown in Figure 1,the irradiance H w below the sea surface andnormal to the beam is

II w = (1 - Ptl)H, sec j.

The radiation that penetrates the surfaceof the sea is progressively diminished as ittravels through the water. By applying Lam­bert's and Beer's laws for monochromaticlight, the intensity H(z) at some depth Zbelow the water surface is given by

J1(z) = l-f w exp [- (a + bW) Z sec j]

where a is the sea-water attenuation coeffi­cient, b is the waste attenuation coefficientand W is the waste concentration. The mini­mum attenuation of sea water occurs at about

540 nm (nanometers) whereas the minimumfor the waste is about 700 nm. The attenua­tion coefficients can be divided into attenua­tion due to absorption and attenuation dueto scattering. In solutions with small par­ticles, blue light has the maximum scatterand in solutions with larger particles allcolors are scattered about the same amount.

By definition of the volume scatteringfunction B(ex), the scattered light intensitydJ from the scattering volume dV in the di­rection that forms an angle ex with the inci­dent beam is

dJ = Fl(z)B(a)dV.

For Mie scattering the intensity of thesca ttered ligh t is proportional to the particl esurface area exposed to the inciden t beam.The intensity of the scattered light is propor­tional to the waste concentration. The vol­ume scattering function varies with bothangle ex and the waste concentration. For avertical photograph taken with an aerialcamera with six inch focal length when thesun's zenith angle is 55 degrees, the angle exwould vary from about 110 to 170 degrees.

As shown in Figure 1, R is the distancefrom the volume element dV to the pointwhere the scattered light strikes the surfaceand dQ is the solid angle formed at the surfaceby dV, then

dV = R 2dfldR.

As the intensity of the light which is scatteredfor the second time is approximately threeorders of magnitude less than the directlighting, the addition of the rescattered lightto the emerging ray from the incrementalvolume will not be considered. The intensityof the emerging ray dJ will be reduced byabsorption and scatter of the water and pal­tides. From the inverse-square law, the ra­diance Nw from the scattering volume at thesurface is

dN w = (d.1/dfl) exp [-(a + bW)R]/R2.

Combining equations,

Hocosiexp [-A seci - (a + bW) (secj + seci2)Z] [(1- Pa)B(ex)dZJ.d.Yw = .

cos i 2 cos J

If the waste concentration is not a function of depth, the resulting equation can be in.te­grated with respect to Z. Letting exp [- (a+bW) (secj+sec i 2)Z») approach zero, the equatIOnbecomes

Ho cos i B(ex) (1 - Po) exp (- A sec i)

cos i 2 cos j (a + bTiV) (sec i 2 + sec j)

OCEAN OUTFALL DISPERSIOX 1243

Upon passing through the sea-air interface some light is reflected and the radiance spreads intoa larger solid angle. 2

The radiance from the sea is

(1)

where n is the refractive index of water and Pw is the reflectivity at the surface.The light reaching the camera is composed of sea surface reflection, path luminance in the

atmosphere and light from the sea. Assuming the photograph \\'as taken so as to avoid thedirect sunlight reflection from the water surface. the surface reflection would be predominantlyblue.

Writing Equation 1 for both the red and green light at the sea surface, and taking the ratioN T / No,

K1B,.(0I)(ao+ boW)exp [(A o - AT) Sec i]R = --------------------

BO(OI) (a, + brW)(2)

where K 1 is a constant and the subscripts rand g refer to the red and green bands, respectively.The ratio of the volume scattering functions shows the effect of scattering on the composition

of the scattered light. As the particle size is relatively large compared to the wavelength oflight, the scattered light is of nearly the same composition as the incident light and this ratio isapproximately equal to one.

Equation 2 can be rewritten as

(3)RA = R exp [(AT - A,,) sec i]aT + bTW

K.\----ay + b"W

The term (AT-Au) sec i is a constant for a photograph but give~ the change in the compositionof the inciden t light as a function of the sun's zenith angle. I t is included in the computations sothat results from photographs taken at different times will be comparable.

The next several paragraphs will be devoted to developing a relationship between the filmdensity and RA. As shown in Figure 2 letj2 represent the angle between the ray to the cameraand the vertical. Let the angle between the ray and the camera axis be represented by c, then bygeometry

dA = dA' (~)2(~)3f COSj2

where dA is the area on the sea surface included in the densitometer aperture area dA' on thephotographic film, Zo is the flying height and f is the focal length of the camera. The solidangle subtended by the lens of diameter Dis

7r (D cos h)2drt = - ---- cos c.4 2 0

The radiant flux dP' collected by the camera lens is

dP' = jVdA COSj2 exp [-E sech]drt.

The irradiance of the film image! is

dP' K 2TrlY cos4 c exp [-E sech]H' = -- = ---------------

dA' (FNO)2

where [(2 is a constant, Tr is the lens transmittance, N is the object radiance at the sea surface,c is the angle between the ray and the camera axis, FNO is the relative aperture (f/ D) of thelens, and E is the extinction optical thickness for the attenuation by the atmosphere from thesea surface to the camera.

1244 PHOTOGRAMMETRIC ENGINEERING

The photographic exposure EX is a product of image irradiance H' and the duration TIM.The relationship between film density and the exposure is shown by the film's characteristiccurve. The curve is a plot of the log exposure vs film density for a particular development. If theexposure of the film is on the straight line portion of the curve, then the film density can beexpressed by

D(x, y) = M + G in (EY).

D (x, y) is the film density at the point on the photo with film coordinates x and y, M is aconstant representing film speed, G is a constant representing film contrast, and EX is theexposure. By combining equations, the radiance from the sea is

K 3(FNO)2 exp [D(x, y)/G + E secj2]iV" =

TIM Tr cos4 c

The ratio of the radiance in the red and green bands is

(4)

Characteristic curves for the films used on the project indicated that the gamma G is nearlythe same for the red and green sensi tive layers.

Equations 3 and 4 can be combined to give the relationship between the film density and thewaste concentration. If R ph is defined as

R ph = expf[Dr(x, y) - Do(x, y)J/G + (E, - Eo) secj2 + (A r - A y) sec i} (5)

and R pho is the value of this ratio when no waste is present, then

(6)

FIG. 2. Geometry of exposure calculation.

Camero

\

I \c/I \\I \~

2:0 1 \~

I \"1

II1

II

where R pho is the ratio determined from Equation 5 for points outside the waste field and R ph isthe value from Equation 5 for points within the waste field. A stepwise regression analysis ofEquation 6 has shown that only the first two terms on the righ t are significant.

FIELD WORK

Data utilized for this paper were acquiredduring the summer of 1968. The general pro-cedure employed in the collection of the datawas to take aerial photography of the wastefield and simultaneously sample the plumefrom a boat by conventional procedures.

Accurate control of the positioning of theboat and the orientation of the photographywas essential. Concentrations determinedfrom aerial photography were compared tothose measured from the boat by matchingground coordinates. To eliminate the possi­bility of discrepancies in concentration beingcaused by error in positioning, an accuratecontrol network was established on shore.Also a network of ten photo control buoyswas established about the outfall area in sucha way that each photo would contain a mini­mum of three buoys. The position of the buoysand the boat was determined by triangula­tion from two shore stations. The boat's po­sition while sampling was determined at one­minute intervals.

Rhodamine vVT tracer was metered intothe pipeline on shore. The concentration of

OCEAN OUTFALL DISPERSIO)i 1245

this tracer in the waste field was measured bytwo continuous flow-through fluorometerssampling from two depths. Before photog­raphy, floats were set to measure the watercurrents. The floats were orange in color, fourfeet square and two inches thick. A droguewas attached to each float.

Photography was taken at t\\'O altitudes.Precise mapping cameras and color film wereused, The small-scale photography (1: 12,000)was intended to be used for buoy location byanalytical strip bridging; ho\\'ever, if Il'asfound more convenient to triangulate thebuoys from shore stations. The low-altitudephotography was taken at a scale of 1 :6,000.The film was processed with a re-wind filmprocessor.

REDUCTIOK OF DATA

Because of the large volume of data, it wasessential that plotting and computations becomputerized wherever possible. Boat con­centrations were computed and stored on filefor comparison with the photo values. Three­dimensional computer plots of the boat con­centrations are shown in Figures 3 and 4.The program was revised to include the boat'strack in Figure 4. On the plots are severallocations within the plume where the concen­trations were measured twice at one point.The differences are 4, 2 and 4 units in Figure3 and 9, 13, 11 and 0 units in Figure 4. Thesediscrepancies in the boat concentrations indi-

cate that the plume had not reached a steadystate.

Photographic information was convertedto digital data with a photo densitometer.The densitometer Il'as equipped with filtersfor measuring the density of the three layersof the color transparency, The vol tage ou t­pu t of the densi tometer wen t to a digi tal vol t­meter for conversion to BCD. The vol tmeteroutput was wired into an x, y, z digitizer as thez value. An aerial fil m holder was attached toa coordinatograph for measurement of thex, y photo coordinates. The digi tizer was con­nected to a card punch. One card was re­quired for each point and contained photoidentification, point number, x and y co­ordinates, and densitometer voltages for thethree spectral bands of the photograph.

The computer program used for the re­duction of photographic data was dimen­sioned to process information from two flightsover the area and up to three photos for eachflight. Photographic orientation was accom­plished by a non-linear solution to the collin­earity condition equations. A published pro­gram for resection3 Il'as modified as a sub­routine for this phase of the computations,The position vector based on the state planecoordinate system was determined by mul­tiplying the photographic vector by the in­verse of the orientation matrix. The sun'saltitude and azimuth were computed fromstandard surveying formulas. Voltage output

'"

-.-

FIG. 3. Plot of boat concentration on August 8, 1968.

1246 PHOTOGRAMMETRIC ENGINEERING

ulRPH~T~ uNuLYS1S &F ~CEuN SUTFuLL D1SPERSI~

FIG. 4. Plot of boat concentrations on August 16, 1968.

of the densitometer was related to the den­sity by fitting a cubic polynomial to densitymeasurement made on a calibrated grayscale.

Atmospheric attenuation coefficients (A r

and A o in Equation 5) were determined fromReference 5 for a standard atmosphere. Thevalue of (Er-Eo) in Equation 5 was approxi­mated by

1~, - /.:. = - 0.024 In (Zo/3280. + 1.)

where 2 0 is the flying height in feet. Values ofRpho in Equation 6 were determined fromthe following regression model:

Rphu = Eo + B1(SUNR) + Ih(Nb) + e.

The regression coefficients B., B1 & B 2 weredetermined from a least squares fit of datafrom points outside the waste field. SUNR isthe angle between the ray to the camera andthe reflected direct sunlight and Nb is theradiance determined from the blue film den­sity.

Values of (Rph-Rpho) were computed foreach data point on the aerial photos andstored in an array oriented about the wastefield. The two indices of the array were re­lated to the ground coordinates of the ele­ment. Each element represented a 60-footsquare area on the sea. After the film densitymeasurements were converted to (Rpl, - Rpho)

\'alues, mlssll1g values in the array were in­terpolated from adjacent points.

Boat concentrations were interpolated at60-foot in tervals along the boat's path andmatched by ground coordinates with thephoto values in the array. A least-squaresregression analysis was made on the datawith the model

W = Cl(Rph - Rpho) + C.(Rph - Rp l.)2 + e (7)

where W is the waste concentration in milli­liters per liter and C1 and C2 are regressioncoefficients. Comparisons of waste concen­trations measured from the boat with thosedetermined from Equation 6 are shown inFigures 5 and 6.

Listed in Table 1 are the values of the re­gression coefficients in Equation 7 and theirstandard error. It can be seen from the tablethat on August 8 C2 was generally the mostsignificant in the relationship between thewaste concentration and (Rph - Rpho) , whereason August 16 C1 was the most significant.During the first day, the tracer concentra­tion was four times as large as in the secondday and was visible to the eye. The coef­ficients for the high-altitude photographyare larger than those for low-altitude pho­tography because of contrast attenuationcaused by light path radiance. The standarderrors of the waste concentration listed in

OCEAN OUTFALL DISPERSION 1247

70

~L:~-~

/40 ISO IGO /70

10 20 50 60

PaSlnON NUMBERS AT 60 ,or INTERVALS

<:

OIO~/\, \

"-:5 /",- -\/,--_ ..... / \« . " ,_/ ---Q: 0 •h IV 80 90 100 /10 /20 /30 /40

<:

'""<:C>

'-.J

Fig. 5. Comparison of boat and photo concentrations August 8, 1968.

Table 1 are significantly less than the dis­crepancies within the boat concentrations ata 95 percen t confidence level. The boat val uesare subject to larger variations as they repre­sent the concentration for a point whereas thephoto values represent the concentration for avolume. The correlation coefficients betweenthe boat and photo concentrations rangedfrom 0.88 to 0.91.

After the coefficients in Equation 7 aredetermined, waste concentration throughou tthe array are computed. These are displayedas a symbolic plot on the line prin ter. Figure7a shows a plot from photographs takenAugust 8 and Figures 8a and 8b show twoplots from photographs taken August 16. Thesymbols represent different ranges in con­centration and were selected so that the

density on the plot increases with the con­centration.

The plot in Figure 7b was made on the com­jJuter controlled calcomp plotter from thedata shown in Figure 7a. The symbolic plotfrom the line printer is distorted as thelongitudinal scale is larger than the lateralscale.

Once the concentrations in the plume areknown, diffusion coefficients are computedthroughou t the waste field. One-dimensional,steady-state diffusion coefficients are de­termined from each set of photos coveringthe field. The non-steady state diffusion coef­ficients are determined by comparing con­centrations computed from two flights overthe area.

Figure 8c is a plot of the concentrations

/20

1(;0

40 SO '0~o FT. INTERVALS

.30

" 20 PHOTO

"r-

" 10 ~ ~

,-

~ ~~

,,~

,-\ ...

;, 00 10POSITION

30 II<: ,\

v\,a \

I

" I

« .0

ll:

" 060

;,

'"<.J 20<:C>

10I

'-.J /

0'20

FIG. 6. Comparison of boat and photo concentrations August 16, 1968.

1248

Day

Aug.8

Aug.16

PHOTOGRAMMETRIC ENGINEERING

TABLE 1. STATISTICAL ANALYSIS OF PHOTO CONCENTRATIONS

Standard ErrorDeg.Time Scale Photo No.'s CJ* C2*

C, Co W Free.

17:21 1:6,000 11,12 (-0.8) 374 7 55 2.3 17217:31 1: 6,000 18,19 (-6.7) 424 8.2 69 2.7 19517:42 1: 6,000 25 58.3 425 12 .8 167 " .7 H2

15:52 1:12,000 3,4 195 (746) 35.5 493 6.2 17816:00 1: 6,000 10,11 146 (205) 21.9 219 5.6 15616: 14 1:6,000 17,18,19 120 (416) 26.6 274 6.3 187

*( ) indicates that the coefficient does not significantly reduce the error.

shown in Figure 8a minus those shown inFigure 8b. Areas on the plot having dif­ferences greater than six units were cross­hatched. The outlines of the plumes are alsosketched on this plot. I t can be seen that theplume had changed considerably during this22 minute period between the flights. Themean difference in concentrations for thiscomparison was 1.8 units with an absolutemean of 4.6 and a standard deviation of 5.9units. The comparison was based on 2,485points within the plume of each flight. Asthe concentration gradients were high, a

small change in the plume posItron resultedin a relatively large apparent discrepancy inconcen tra tions.

SUMMARY

The conventional method for measuringthe dispersion of waste from an ocean outfallis by sampling from a boat. Because the out­falls are generally located on the relativelyshallow coastal shelf, field work in this near­shore area is impossible much of the timebecause of rough seas. Aerial photographyoffers a possible method for evaluating waste

!(a) symbolic plot ( b) iso-concentration plot

FIG. 7. Waste concentrations from aerial photography August 8, 1968.(a) Symbolic plot. (b) Iso-concentration plot.

OCEAN OUTFALL DISPERSION 1249

ee)Concentration difference

Photos I7'18~'~/9,,-~J~L~J~.16: 14 ~

Photos 3,415:52 -

'--_l:lt,l::c:

AUGUST 16.1.9F..q

c!lJNeqativeDifference

&PositiveDilference

(b)

Photos 17,18 &19(a)

Photos 3 &4

FI<;.8. \<\Taste concentrations determined frolll aerial photography August 16, 1968.(a) Photos 3 and 4. (b) Photos 17, 18 and 19. (c) Concentration difference.

concentrations, dispersion processes, andcurrent patterns in the outfall area.

Color photography was used to measurethe reflected light from the waste in the sea.A relationship between the image densities ofthe color photography and the effluent con­centration in the waste field was developed.

Field studies were conducted simulta­neously through observations of the oceanoutfall waste plume by aerial photographyand conventional boat sampling. The photo­graphic method was evaluated by comparingthe concentrations determined from thephotography with those measured by boatsampling.

Correlation coefficients between the boatconcentrations and the photo concentrationswere about 0.9. The discrepancies betweenthe two methods are not entirely due toerrors in the photographic procedure butalso includes movement of the waste plumebetween the time of boat sampling and the

aerial photography. The boat sampling wasconducted over a two-hour period and rep­resents a composite of plume patterns duringthe sampling period.

CONCLUSION

It is realized that in this initial attempt todevelop a color aerial photographic analysistechnique to measure waste concentration inan ocean outfall, many simplifying assump­tions were necessary. Because of these as­sumptions, the relationship between wasteconcentration as derived from the photo­graph and boat concen tration measuremen tsis open to criticism. Teverthelses, we have de­veloped a technique and have identifiedareas which, through additional research,may result in a precise method for determin­ing outfall waste concentrations remotely. Inaddition, we have shown how such data,once obtained, can be subjected to computeranalysis and displays of results generated.

1250 PHOTOGRAMMETRIC ENGINEERI G

ACKNOWLEDGEMENT

This research is sponsored by the FederalWater Pollution Control Administration(project 16070 ENS) and was conductedwith the cooperation of the Georgia PacificCorporation and the International PaperCompany. The authors wish to acknowledgethe efforts of the 34 students, staff membersand persons from the Pacific orthwestWater Laboratory who have contrihuted tothe project.

REFERENCES

1. Jensen, N., Optical and Photographic Recon-

naissance Systems. New York, John Wiley andSons, 1968.211 p.

2. Jedov, N. G., Optical Oceanography. Amster­dam, Elsevier, 1968, 194 p.

3. Keller, M. and G. C. Tewinkel, Space Resectionin Photogrammetry. Washington, D.C., 1966.9 p. (Coast and Geodetic Survey TechnicalBulletin 32)

4. Silvestro, F. B. and K. R. Piech, DevelopmentoC Aerial Photography as an Aid to WaterQuality Management. Cornell AeronauticalLaboratory Final Report I o. VT-2614-0-1.January 1969.

5. Valley, S. L., Handbook of Geophysics and SpaceEnvironments. Air Force Cambridge ResearchLaboratories. 1965.

M1971 CONVENTIONWASHINGTON, D.C.MARCH 7-12

The 37th Annual Meeting of the American Society of Photogrammetry will be

held at the Washington Hilton Hotel, Washington, D.C., March 7-12, 1971 as

part of the 1971 ASP-ACSM Convention. The ASP Technical Program will

feature papers reflecting recent developments in:

Photogrammetric Techniques and Instrumentation

Aerial Photography

Remote Sensing

Photo Interpretation

Analytical Photogrammetry

Non-Topographic Photogrammetry

. Photogrammetric Applications

For further information write to American Society of Photogrammetry, lOS N. Vir­ginia Ave., Falls Church, Va. 22046.