Av_physics Of Aerial Photography

PHYSICS OF AREAL PHOTOGRAPHY Lecture Lecture55 First FirstYear YearStudents Studentsof ofSP SP

Prof. Prof.Anjana AnjanaVyas Vyas th 11 11th September September2008 2008

COVERED TILL DATE ON REMOTE SENSING 1.DEFINATION 2.ADVANTAGES OF R S 3.PLATFORMS 4.SATELLITE CHARACTERISTICS 5.REVOLUTION AROUND EARTH 6.ELECTROMAGNATIC RADIATIONS 7.RESOLUTION 8.IMAGE INTERPRETATION KEY

COVERED TILL DATE ON GIS 1.INTRODUTION TO GIS 2.SPECIAL FORM OF Info Sys 3.IMPORTANT ASPECTS OF GIS 4.EXAMPLES OF SPATIAL AND NON-SPATIAL DATA BASE 5.QUESTIONS GIS CAN ANSWER 6.CASE STUDY ON RURAL INFORMATION SYSTEM

TODAY WE WILL LEARN ABOUT PHYSICS OF AERIAL PHOTOGRAPHY

The term "photography" is derived from two Greek words meaning •"light" (photos) and •"writing" (graphien)

Definition Definition :: An aerial photo is just a black and white (b & w) or color "picture" of an area on the Earth's surface (plus clouds, often), either on print or on transparency. A film camera shoots the picture from a free-flying platform (airplane, helicopter or balloon) some preplanned distance above the surface.

DEFINITION OF PHOTOGRAMMETRY

Photogrammetry is the art, science, and technology of obtaining reliable information about physical objects and the environment through the processes of recording, measuring, and interpreting photographic images and patterns of electromagnetic radiant energy and other phenomena. (Mapping Sciences by the American Society for Photogrammetry and Remote Sensing (ASPRS))

 

DEFINITION OF PHOTOGRAMMETRY

The science or art of obtaining reliable measurements by means of photographs (Third Edition of the Manual of Photogrammetry)

It should be noted that the term art is applied as meaning skill which is obtained through experience. (Manual of Photogrammetry, Fourth Edition, published in 1980 by the ASPRS.)

Boston by Black and King (1860)

Oblique aerial photograph of downtown Boston obtained by Samuel A. King and J. W. Black from a balloon at an altitude of 1,200 ft. on October 13, 1860. • First aerial photograph taken from a captive balloon in the United States.

Eye Eye

COMPARISION COMPARISION

Retina

Retina Retina

Lens Lens Object Object

Image Image

HUMAN HUMANEYE EYE

Iris Iris

Film Plane

FilmPlane Plane Film

Camera Camera

BetweenBetweenthe-lens the-lens shutter shutter

Lens Lens

Image Image

Roll Roll of offilm film

Focal FocalLength Length

Object Object

Aperture Aperture

OPTICAL OPTICAL CAMERA CAMERA

Types of aerial photographs 

Orientation of photo  Vertical  Oblique  high and low oblique



Spectral characteristics of film  Black and White (panchromatic)  Black and White IR  UV  Color  Color IR



Scale of photo  A photo is considered to be “large scale” if the ratio of distance units on the photo to distance on the ground is large (ie: 1:2000)



Stereo pairs

PROFESSIONAL PROFESSIONALPHOTOGRAPMMETRY PHOTOGRAPMMETRYORGANIZATION ORGANIZATION The TheAmerican AmericanSociety SocietyofofPhotogrammetry Photogrammetry(ASP) (ASP)founded foundedinin1934 1934 Manual ManualofofPhotogrammetry Photogrammetry Manual ManualofofPhotographic PhotographicInterpretation Interpretation Manual of Color – Aerial Manual of Color – AerialPhotography Photography Manual ManualofofRemote RemoteSensing Sensing Hand HandBook BookofofNon-topographic Non-topographicPhotogrammetry Photogrammetry Photogrammetric PhotogrammetricEngineering Engineeringand andRemote RemoteSensing Sensing The TheAmerican AmericanCongress Congresson onSurveyijng Surveyijngand andMapping Mapping(ACSM) (ACSM)founded foundedin in1941 1941 Surveying and Mapping Surveying and Mapping The TheAmerican AmericanSociety SocietyofofCivil CivilEngineers Engineers Journal Journalofofthe theSurveying Surveyingand andMapping MappingDivision Division The TheCanadian CanadianInstitute Instituteofof Surveying Surveying The TheCanadian CanadianSurveyor Surveyor The International Society The International Societyfor forPhotogrammetry Photogrammetryand andRemote RemoteSensing Sensing(ISPRS) (ISPRS)founded foundedin in 1910 1910 Photogrammetrics Photogrammetrics The TheIndian IndianSociety Societyofof Remote RemoteSensing Sensing The TheIndian IndianSociety SocietyofofGeomatics Geomatics The Indian National Cartographic The Indian National CartographicAssociation Association

USE USEOF OFPHOTOGRAMMETRY PHOTOGRAMMETRY

Planning Planningand andDesigning DesigningHighway Highway Rail Railand andRoads Roads Rapid Transit Rapid TransitSystem System Bridges Bridges Pipelines Pipelines Aqueducts Aqueducts Transmission TransmissionLines Lines Hydroelectric Dams Hydroelectric Dams Flood FloodControl ControlStructures Structures River Riverand andHarbor HarborImprovements Improvements Urban UrbanRenewal RenewalProjects Projects

Astronomy Astronomy Architecture Architecture Archeology Archeology Geomorphology Geomorphology Oceanography Oceanography Hydrology Hydrologyand andWater WaterResource Resource Conservation ConservationEcology Ecology Mineralogy Mineralogy

Non NonEngineering EngineeringApplication Application Plot PlotMaps Maps Soil SoilMaps Maps Forest ForestMaps Maps Geologic GeologicMaps Maps Maps Mapsfor forCity, City,Regional RegionalPlanning Planningand andZoning Zoning

Aerial Aerial Camera Camera Lens Lens Angle-of-View Angle-of-View

22,0,00000f ft t

44°0°0 11, ,00000f 0ft t

44°0°0 77°0°0 99°0°0 111100° ° aa. .

44°0°0

bb. .

Types of Distortion Caused by Aircraft

Roll

Pitch

Yaw

Distortion caused by roll, pitch and yaw

PHOTOGRAMMETRY DISTINCT AREA

Metric Photogrammetry Use of measurements made on aerial photographs to obtain quantitative data about earth's surface. •Distance •Angles •Areas •Volumes •Elevations •Sizes

PHOTOGRAMMETRY DISTINCT AREA

Interpretative Photogrammetry Aerial photographs or images produced by electronic sensors are carefully studied to produce an interpretation of the conditions. •Photographic Interpretation •Photographic Images •Remote Sensing •Multispectral Camera •Infrared Camera •Thermal Camera •Side Looking Airborne Radar Shape, size, pattern, shadow, tone & texture used to identify objects

Profile ProfileView Viewof ofAAMetric MetricCamera Cameraand andSystem SystemComponents Components P la e P lta tn en vv ac u u m acuum fiflim lm flfa t t e n er latten er

T ak eu pp T ak e -u re re elel

U nn ex pp oo se U ex sd ed fiflim r e e lm relel

F ilim F lm M a g a zz in ee M a g a in F ilim F lm

O pp titc O ia clal ax is ax is

F oo ca la ee F clalp p ln an F o ca F o clal le gg th ,, ff ln en th

C a m ee rr a C a m a B o d y B o d y

L ee n ssC o n ee L n C o n A ss m b ly A se se m b ly L en ss rr ea oo dd alalpp oo in tt L en er arnn in S h uu ttte S h tr er F ilitle F tr er

L en ss L en D ia hh ra m D ip ap rg ag m L en ss frfo nn tt L en ro nn oo dd alalpp oo in tt in

The Thef/stops f/stops for for aa Camera Camera Lens Lens and and the the Size Sizeof of the the Aperture Aperture Openings Openings

f /8 f /8

f / 11 f / 11

f / 5.6 f / 5.6

f / 16 f / 16

f /4 f /4

f / 22 f / 22

f / 2.8 f / 2.8 f / 2.8 f / 2.8

f / stop f / stop

2 .8 4 5 6 2 .8 4 .5 .6

6 2 2 8 1 1 1 6 2 2 8 1 1 1

f=8 0m m f=8 0m m

L ens L ens

4@ f / 5.6 4@ f / 5.6

Photogrammetry



Taking quantitative measurements from air photos  Heights of objects  Areas  Lengths  Density  Etc.

Scale  Scale

is the ratio of the measured length of an object on an image to its real length on the ground  Always expressed as a ratio (e.g. 1:24,000) Small scale means low resolution! Large scale means high resolution!

Calculating Scale for Air Photos

 For

air photos scale depends on:  Focal Length of camera lens (typically 150 mm for air photography but can vary)  Height of camera above ground Scale = Focal Length/Height

Photo Length

Focal Length

Similar Triangles

Height

Ground Length

Calculating scale from photos themselves

 If

you know the length of an object on the photo and its true length, you can calculate scale Scale = length on photo/true length MUST BE CONSISTENT WITH UNITS!!

Vertical Vertical Aerial Aerial Photography Photography VVertica ertical lAAeri eria al l PPhho ototog grarapphh OOv verer LLevevelelTTerra errainin

CCam amera era film p l fil m pan l ane e

AAltit ltitu ud de e ababo ov ve-g e-grorou un nd d- lev levelel(A(AGGLL) )

fiel field d o of fv vi ew i ew

OOp ptical tical axaxi si s

PPrin rincicip palalp po oinint t(P(PPP) ) 9 90 0° °

Goosenecks Goosenecksofofthe theSan SanJuan JuanRiver RiverininUtah Utah

Vertical Photographs Vertical photographs are made using special photogrammetric cameras, that are built into an aeroplane looking straight downwards. While taking the photographs, the aeroplane flies over a certain area in a meandric way, so that the whole area is covered by overlapping photographs. The overlapping parts can be seen stereoscopically (i.e. in 3D) by means of stereoscopes. Most of the vertical photographs, which are stored in our archive, were taken using a Zeiss-Reihenmesskammer.

Scheme of Flight for Vertical Photograph

Vertical Photograph

Vertical Stereo pair with 80% Overlap © Flugbildkompanie Langenlebarn

VERTICAL PHOTOGRAPHY

'False-colour' infrared photograph of saltmarsh, Scolt Head Island, Norfolk (16th October 1986). Film ref. RC8Ki-AQ 75.

Low-oblique Low-obliqueAerial Aerial Photography Photography L L o oww - -OO b bl il qi qu ue e AA e er ri ai al l P Ph ho ot to og gr ra ap ph h OO v ve er r F Fl al at t T T e er rr ra ai ni n

f if ei el dl d o of f v vi ei eww

OO p pt it ci ca al l a ax xi si s 9 90 0° °

HH o or ir zi zo on n i si s n no ot t s sh ho oww n n i ni n p ph ho ot ot og gr ra ap ph h

Low-oblique Low-obliquephotograph photographof ofaabridge bridgeon on the theCongaree CongareeRiver Rivernear nearColumbia, Columbia,SC. SC.

Low oblique (no horizon)

High-oblique High-obliqueAerial AerialPhotography Photography HHigighh- O -Obbliq liquue eAAe er riaial l PPh ho ot otog gr ra apphhOOv ve er r FFlalat tTTe er rr ra ainin

fie f ieldldo of f v vieieww

OOp ptictica al l a ax xisis

HHo oriz r izo on nisis s hs ho owwn nininththe e p ph ho ototog gr arap ph h

9 90 0° °

High-oblique High-obliquephotograph photographofofthe thegrand grand Coulee CouleeDam Damin inWashington Washingtonin in1940 1940

High oblique

OBLIQUE PHOTOGRAPHY

Here is an example of a typical oblique picture made during a Viking Flight in 1950, looking across Arizona and the Gulf of California to the curving Earth horizon Ice-carved corries on the east side of Snowdon, Gwynedd (2 July 1985). Film ref. 70K-EY 8

Today, Today, most most of of the the photographs photographs have have aa format format of of 23 23 by by 23 23 cm. cm. Every Every photograph photograph has has aa strip strip containing containing subsidiary subsidiary information information on on its its border. border.

Annotation Annotationon onthe thePerimeter Perimeterof ofAn AnAerial AerialPhotograph Photograph

Every photograph has a strip containing subsidiary information on its border. a project field (1)

with useful information about when and why the photograph was taken

a clock (2)

which can be helpful, if you don´t know how to orientate the picture (where is the north direction?)

the calibrated focal length which is needed during photogrammetrical (3) analysis; most of our photographs were taken with a focal length of about 150 mm (wide angle) or 210 mm (medium angle) the bubble (4)

showing you, if the photograph is in fact a vertical one

the serial number of the camera (5)

which is needed to identify the right calibration protocol

an altimeter (6)

which is useful to estimate the scale of the photograph

and the number of the photograph (7)

most of the films contain at about 300 pictures

Principal Point

Fiducial marks

Fiducial axes

Principal point

Marginal information

Flight Paths

End lap of Aerial Photographs

Side lap of Aerial Photographs

End lap (or fore lap) is the important bit • It ensures every point on the ground appears in at least two photographs • Distance between principal point of adjacent photographs is known as the “air base”

Verticality is most important as it has minimum distortion and can be used for taking measurements

If you know focal length of camera and height of aircraft above the ground you can calculate the scale of the photograph

Scale = f/H-h f = focal length (distance from centre of lens to film surface)

H H

Scale = f / H-h H = flying height of aircraft above sea level h = height of ground above sea level

When you know the scale you can take 2-D measurements from a photograph (e.g. horizontal distance, horizontal area, etc.)

But to take “true” measurements on an uneven surface you need to work in 3-D

Height of Objects 

Can calculate using measurements that you make on a single photo h = d*H/r h = height of object H = aircraft height above datum r = distance from principal point to top of object d = distance from object bottom to object top

Air Photo Height Calculation

Relief Displacement H’ = H – hA’ H (not shown) = Flying height above datum. ‘

d = distance from bottom to top of object on image. r = radial distance for principal point to top of object. h = height of object from bottom to top.

Datum

CEE 403

hA’

Relief Displacement 





It is actually relief displacement that causes scale variations. Cannot mosaic photos of same object taken at different photo centers even if H’ is constant. Direction of displacement will be different on different photos.

CEE 403

Other methods for measuring height Length

of shadows on photo and knowledge of sun angle Parrallax methods using two photos (requires two overlapping photos)

Measuring Areas on Air Photos  Line

intercept sampling to determine relative area of classes  Use parallel lines spread across image and measure how much (length) of each class on the image is intersected by the line.  Use relative areas and the photo scale to calculate the absolute area.  Random dots  Count the number of random dots in each class to get relative area  Use a computer to digitize polygons around each class and get exact area.

Line Intercept Area Determination

Parallax

Pencil is very displaced because it is close to observer Church is less displaced because it is further away

Parallax is used to find distance to stars, using two viewing points on either side of Earth’s orbit

The same principle can be used to find height of objects in stereo-pairs of vertical aerial photographs

Parallax Height

H = height of aircraft above ground P = absolute parallax at base of object being measured* (photo air base) dP = differential parallax For convenience the photo base length of a stereo pair is commonly substituted for absolute stereoscopic parallax (P)

Human vision Eye base (6-7cm) Human vision is binocular in most cases, and human eyes can resolve parallax as angle of convergence This provides perception of “depth” and enables us to judge distances (up to 400m)

3-D stereo-optic viewing of the Earth’s surface is possible using overlapping pairs of vertical stereo aerial photographs

Two types of light-sensitive cells are present in the retina:

• Cones

are clustered around the fovea centralis • Rods are widely distributed elsewhere

Optical plane

Fovea centralis

Air Photo Interpretation 

Pre-interpretation issues to address  Classification System Anderson LULC  Minimum Mapping Unit (MMU)  Digital vs. Analog system  Date and Type of Photo (s)



Identifying features on the ground by using information depicted in air photos or satellite data  Color (or gray shade); Texture  Pattern; Context (Association)  Shape; Size  Shadow Location Tone

 You

should understand:

 How

aerial photography is collected (Film, flight geometries, etc.)  How to calculate scale  How to make basic measurements (photogrammetry)  How to interpret imagery

Types of Aerial Photography : Black and White – Austin, Texas

Types of Aerial Photography : Black and White – Hindalgo County, Texas

(a) The Pentagon and vicinity, Washington, D.C., portion of a National Aerial Photography Program 18-inch 2 X enlargement, 1:20,000-scale, March 1994

(a) (a)

(b) (b)

(b) The Pentagon and vicinity, Washington, D.C., portion of a National Aerial Photography Program 9inch aerial photograph, 1:40,000-scale, March 1994

The Pentagon and vicinity, Washington, D.C., portion of a National Aerial Photography Program 36-inch 4 X enlargement, 1:10,000scale, March 1994

Aerial Photographs of Jenin - ISRAEL April 2002 The City of Jenin including the Jenin refugee camp prior to Operation Defensive Shield

Enlargement of Jenin refugee camp and combat zone on April 13, 2002, after the battle.

Combat zone (approx. 100m X 100m)

< --

1000 meters (2/3 mile)

-- >

Additional aerial views of combat zone in Jenin refugee camp:

Jenin refugee camp

Relief Displacement H’ = H – hA’ H (not shown) = Flying height above datum. ‘

d = distance from bottom to top of object on image. r = radial distance for principal point to top of object. h = height of object from bottom to top.

Datum

CEE 403

hA’

Relief Displacement  Similar

Triangles:

D R = h H'

(1)

From scale equations:

d f D H' H 'd = ; = ;D = D H' d f f r f R H' H 'r = ; = ;R = R H' r f f

CEE 403

(2) (3)

Relief Displacement Substitute 2 and 3 into 1:  H 'd     f = h

 H 'r     f  ; d = r ; d = rh H' h H' H'

•Relief displacement increases linearly with the the center of the photo.

distance from

•Relief displacement increases linearly with the height object. •Relief displacement increases inversely with the the bottom of the object.

CEE 403

of the

flying height above

Relief Displacement 





It is actually relief displacement that causes scale variations. Cannot mosaic photos of same object taken at different photo centers even if H’ is constant. Direction of displacement will be different on different photos.

CEE 403

Height of Object d=

rh H'

rearranged yields

dH ' h= r

Can get height of object by measuring displacement. Example: H = 4500ft (above datum); Base of tower at 500 ft elevation; Radial distance from pp to top of tower = 3.00 inches; Displacement = 0.100 inches.

H ' = H − htowerbase = 4500 ft − 500 ft = 4000 ft hT =

dH ' (0.100" )(4000' ) = = 133 ft r 3.00" CEE 403

Errors  Determination

of height of tower subject to:

 Photo

not exactly vertical. Systematic Errors  Shrinkage / expansion of photo.  Uncertainty in d.  Uncertainty in r. Random Errors  Uncertainty in H’.

}

}

Systematic errors obey known physical laws and can be corrected (e.g., corrections for shrinkage / expansion). Random errors behave according to the laws of probability. CEE 403

Random Errors Point of inflection

Point of inflection







Normally-distributed random errors have a 68% chance of falling within one standard deviation (± ) of the peak of the curve.



We can determine the impact of random errors in functions of variables using “error propagation”.

CEE 403

Random Errors In the relief displacement problem:



If we know

we can determine



Can isolate each variable (d, r, H’) and see how changes affect hT. Use partial derivatives:  

hT =

dH ' r

σ hT

σ d ,σ r ,σ H '

dH ' ∂hT H ' ∂hT d ∂hT − dH ' hT = ; = ; = ; = r ∂d r ∂H ' r ∂r r2 CEE 403

Random Errors  Effect

of dd:

 H' dhT =  dd  r 

4000 ft   If dd = +0.001” dhT =  (+0.001in) = +1.3 ft  3.00in 

Effect of dH’: d  dhT =  dH ' r

If dH’ = +50 ft

 0.100in  dhT =  (+50 ft ) = +1.7 ft  3.00in 

Effect of dr:  − dH '  dhT =  2 dr If dr = +0.05 in  r  CEE 403

 (0.100in)(4000 ft )  (+0.05in) = −2.2 ft dhT =  2 ( 3 . 00 in )  

Random Errors  Combined

Uncertainty

If Sd = ±0.001”; SH’ = ±50’; Sr = ±0.05”, What is the uncertainty in hT? 2

S hT

2

2

 ∂h   ∂h   ∂h  =  T  S d2 +  T  S H2 ' +  T  S r2  ∂d   ∂H '   ∂r  2

2

2

 H' d   − dH '  =   S d2 +   S H2 ' +  2  S r2  r  r  r  2

2

2

 − (0.100in)(4000 ft )   4000 ft   0.100in  2 2  (0.05in) 2 =   (0.001in) +   (50 ft ) +  2 (3.00in)  3.00in   3.00in    = ±2.8 ft ≅ 3 ft

CEE 403