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Selected Characteristics of NRI Aerial Photos

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Presentation on theme: "Selected Characteristics of NRI Aerial Photos"— Presentation transcript:

1 Selected Characteristics of NRI Aerial Photos
… a brief introduction …

2 Characteristics of NRI Aerial Photos
A Few Selected Terms Formats, Spectral Sensitivity, and Scale Scale, Flying Elevation, and Footprints Fiducials and Other Photo Markings Intro to Photo Geometry and the Single Point Perspective Resolution Orientation of Photos for Scanning Use, Care and Storage of Photos

3 A Few Aerial Photo Terms
Frame (also known as Metric or Mapping) Cameras Shutter exposes the entire frame at a single instant Calibrated in a laboratory to determine internal geometry focal length lens distortion 9 inch by 9 inch film NRI aerial photographs are acquired with a tested and calibrated camera. Camera used must have a current USGS camera calibration test report (current means no more that 3 years old). Frame, Metric, or Mapping Camera: A camera that has been calibrated in a laboratory to determine its internal geometry including the focal length, lens distortion, principal point, and fiducial coordinates. Photo Characteristics

4 A Few Aerial Photo Terms
Focal Length Distance (along the optical axis) from the camera lens to the plane of sharpest focus Lens Focal length Most NRI photographs are acquired with a 6” (153 mm) focal length lens. Focal length: Distance along the optical axis from the camera lens to the plane of sharpest focus. Photo Characteristics

5 A Few Aerial Photo Terms
Vertical Photography Camera axis is < 3° from vertical Oblique Photography Camera axis is > 3° from vertical Low oblique—no horizon High oblique—includes horizon Camera Axis NRI aerial photos are acquired in the vertical orientation over the center of the sample site. NRI photo contract specifications allow for a tilt of no more than 4 degrees. Vertical photography: Photographs taken from vertical or near vertical positions. Photo Characteristics

6 Aerial Photo Formats, Spectral Sensitivity & Scale
Color film positive One photo per NRI site Monoscopic Spectral Sensitivity: Natural color Color Infrared Scales: 1:7,920 1:12:000 1:15,840 NRI photos are color film positives (also known as transparencies). The film delivered to NRCS is the original film from the camera. This is the one and only copy and is irreplaceable if lost. Recent NRI photography is all natural color, but some CIR has been collected in the past and CIR is an option on the current contract. All NRI photos attempt to acquire the entire site and a buffer on one piece of film. For a nominal 160 acre NRI site, the area segment will be centered in the photo with a ¼ mile buffer on all sides. As segment sizes increase in area beyond 500 acres, the photo scale changes to 1:12,000 to acquire the entire NRI site on one photo. There are a handful of NRI sites larger than 900 acres that require a 1:15,840 scale photo. Color film positive: A photograph on a transparent base processed to produce an image that reproduces the colors of the original scene, as opposed to a negative which is a complement of the original scene. Natural color: Colors as scene by the human eye. Color Infrared: Film that is sensitive to infrared wavelengths. Infrared wavelengths are displayed as red, red light is displayed as green, green light is displayed as blue, and blue light is eliminated by a filter. Scale: Ratio of a distance displayed on a photo with its corresponding distance on the ground. Photo Characteristics

7 Scale, Flying Elevation, and Ground Distance
7,920 ft Photo Scale = focal length/height above ground 1:7,920 = 6”/3,960’ 1:12,000 = 6”/6,000’ 1:15,844 = 6”/7,920’ Ground Distance = Photo Distance/Photo Scale 5,940’ = 9”/1:7,920 9,000’ = 9”/1:12,000 11,880 = 9”/1:15,840 lens elevation 6,000 ft Shown are the changes in the ground distance of 9”x9” NRI photos acquired with a 6” focal length lens at different flying heights. Photo scale: focal length/height above ground Ground distance: photo distance/photo scale 3,960 ft Not to scale 5,940’ 9,000’ 11,880’ Photo Characteristics

8 Photo Footprints Footprint: the perimeter of the area covered by an aerial photo. Large Scale Footprints (small area covered, features appear large) Small Scale Footprint (large area covered, features appear small) Footprint: The perimeter of the area covered by an aerial photo. Map Photo Characteristics

9 NRI Aerial Photography Footprints
Approximate Coverage of NRI Photos 1:7,920 5,940’ x 5,940’ 810 acres 1:12,000 9,000’ x 9,000’ 1,860 acres 1:15,840 11,880’ x 11,880’ 3,240 acres Nominal 160 acre area segment This slide shows the approximate coverage of NRI photos at the scales used. The 1:7,920 scale is used for most NRI photos. Once an area segment exceeds 500 acres (300 acres in California and Missouri because of some rectangular shaped area segments), the 1:12,000 scale is used. For a handful of area segments over 900 acres, the 1:15,840 scale is used. Photo Characteristics

10 Fiducials Fiducials: permanent reference points exposed onto the photograph. Principal Point (PP): Center of photo—found by intersection of lines drawn between opposing fiducials. The appearance of fiducials varies by camera. Some are bull’s eyes and some are cross hairs. Fiducials: Permanent reference points exposed onto the photograph. Principal Point: Center of the photo found by intersection of lines drawn between opposing fiducials. Nadir: The point directly below the airplane at time of the photo. Nadir: image of point directly below airplane at time of photo (Nadir will equal PP for vertical photos). Photo Characteristics

11 Other Photo Markings - Data Strip
Data Strip: varies in appearance and location by camera, but usually contains an altimeter and clock. Data Strip: A strip on the margin of a photo containing information such as altimeter and clock images. altimeter clock Photo Characteristics

12 Other Photo Markings—Standard Title Block
State County State FIPS Code Agency Name Date Segment # Nominal Scale to nearest 1000. Not to be trusted for measurements! Standard titling required on North edge of NRI photo. Some vendors have permission to use automated titling systems that differ from the above example. NOTE: Standard title block info is oriented to the North on NRI photographs. Photo Characteristics

13 Other Photo Markings—Automated Title Block
EXAMPLE 1 Time FIPS Segment # North Arrow Date State Agency Name Nominal Scale to nearest 1000. Not to be trusted for measurements! County Example of automated titling. Photo Characteristics

14 Other Photo Markings—Automated Title Block
EXAMPLE 2 State Date Latitude and Longitude of photo center FIPS North Arrow Segment # Agency Name Nominal Scale to nearest 1000. Not to be trusted for measurements! Another example of automated titling. This one includes the latitude and longitude of the photo center. Photo Characteristics

15 Other Photo Markings—Camera # and Focal Length
EXAMPLE 1 Other Photo Markings: vary in appearance and location but usually include calibrated lens focal length, camera number, and/or lens number. The camera # or lens # is needed to find the camera calibration report. The camera and/or lens number is needed to locate the right camera calibration report. The location of the camera number, lens number, and focal length vary. All three may or may not be present. Camera number: Serial number of the camera that took the photo. Needed to find the USGS Report of Calibration. USGS Camera Calibration Report: A laboratory report, required every 3 years, with precision measurements of the internal geometry of the camera, focal length, and lens distortion. Camera # Focal length mm Photo Characteristics

16 Other Photo Markings—Camera #
EXAMPLE 2 Other Photo Markings: vary in appearance and location but usually include calibrated lens focal length, camera number, and/or lens number. The camera # or lens # is needed to find the camera calibration report. The camera and/or lens number is needed to locate the right camera calibration report. The location of the camera number, lens number, and focal length vary. All three may or may not be present. Camera # Photo Characteristics

17 Other Photo Markings—Camera # and Focal Length
EXAMPLE 3 Camera # Focal length mm Other Photo Markings: vary in appearance and location but usually include calibrated lens focal length, camera number, and/or lens number. The camera # or lens # is needed to find the camera calibration report. The camera and/or lens number is needed to locate the right camera calibration report. The location of the camera number, lens number, and focal length vary. All three may or may not be present. Photo Characteristics

18 Photo Geometry--Single Point Perspective
NRI photos contain image displacement. In this slide the buildings lean outward in the single point perspective view. Because NRI photography is exposed over the center of the area segment, image displacement is minimized. However by orthorectifying NRI photography, displacements caused by topography and camera orientation over the entire photo are removed. Orthographic perspective: View in which light rays all travel vertically and do not converge through a lens. Single point perspective: View that results when light rays are focused by a lens. Oblique perspective: View that results when objects are viewed from a non-vertical position. Photo Characteristics

19 Photo Geometry--Single Point Perspective
Photo scale varies with relief and objects at different elevations are displaced relative to one another, thus distances and bearings are more difficult to measure directly: If scale and orientation are known, distances and bearings can be measured directly: Orthorectification improves the accuracy of length and area measurements on NRI photos. Photo Characteristics

20 Photo Geometry--Single Point Perspective
The photo scale is different at the tops of the buildings than at the street level. The tops of the building are displaced radially outward relative to their location at the street.

21 Photo Geometry--Single Point Perspective
More than just buildings… The clearcut boundaries (right) are straight lines on the map and ground Higher elevations are displaced radially outward (relative to lower elevations)

22 Photo Geometry--Single Point Perspective
Distortion: error resulting from lens imperfections, camera tilt, poor camera vacuum, etc. Displacement: the result of projecting a 3-D world (with varying heights) on a 2-D surface from a single point perspective. Allows for stereo viewing, however, NRI photos are not acquired in stereo Orthorectification: For the NRI, scale variation, relief displacement, camera orientation, and lens distortion must be removed for accurate measurement of lengths and areas. Distortion: Error resulting from lens imperfections, camera tilt, poor camera vacuum, etc. Displacement: The result of projecting a 3-D world (with varying heights) on a 2-D surface from a single point perspective. Orthorectification: The process of removing geometric errors caused by relief displacement, camera orientation, and lens distortion. Photo Characteristics

23 Photo Geometry--Orthorectification
The image on the left is the original single point perspective NRI photograph. After removing the distortion and displacements through orthorectification, the result is a photo map that can be used for accurate measurement of lengths and areas. Original Photo Orthorectified Photo Photo Characteristics

24 Resolution of Aerial Photography
Smallest feature which can be detected With film, resolution is expressed as Line pairs per millimeter (lp/mm) or Ground Resolved Distance (GRD) Photography has the most resolving power of any remote sensing system Mapping frame cameras and films used for the NRI under ideal conditions can typically resolve about 100 lp/mm GRD = reciprocal of image scale/system resolution. Example: the calculated GRD of a 1:7,920 NRI photo is 7,920/ (100 lp/mm) = GRD 79.2 mm or 3.1 inches Digital or scanning resolution is expressed as Ground Sample Distance (GSD) which is the size of the pixel in ground units GSD = reciprocal of image scale/scanning resolution Example: the calculated GSD of a 1:7,920 NRI photo is 7,920/600 dpi = GSD 13.2 inches Resolution: The smallest feature which can be detected. Resolution is a difficult term to define in a practical sense. A system can be tested in a lab and used to compare it with other systems. When used for natural resource interpretation, we want to detect objects, but also identify and interpret them. In addition, the resolution on a delivered photo may be poorer than determined mathematically because of haze, smoke, vibration, and contrast of the targets. Ground Resolved Distance: A term used to express the combined effects of scale and system resolution. Ground Sample Distance: A term used to express the size of a pixel in ground units. Photo Characteristics

25 Resolution of NRI Photos at Various Scales
GRS 100 lp/mm GSD 600 dpi scan 7,920 3.1” 13.2” 12,000 4.7” 20.0” 15,840 6.2” 26.4” Table showing the mathematically calculated GRS and GSD of NRI photography at different scales. These numbers may not represent the actual resolution because of factors that include atmospheric conditions (haze and smoke), motion, vibration, illumination, and contrast. Photo Characteristics

26 MicroTeck 9800XL Scanner Considerations
Standard desktop scanners like the MicroTek 9800XL can do an excellent job of scanning NRI photography. Limitations of desktop scanners for NRI include: Less geometric accuracy than photogrammetic scanners No option for unattended roll film scanning Advantages of desktop scanners for NRI include: Cost $1,800 vs. $100,000+ for a photogrammetric scanner Geometric accuracy acceptable for natural resource projects The MicroTek is capable of scanning at 1,600 dpi, but testing has shown that 600 dpi is adequate for the NRI. Desktop scanner: A relatively low cost scanner typically connected to a personal computer. Photogrammetric scanner: A scanner capable of high image quality and positional accuracy. Photo Characteristics

27 Orientation of Film on the Scanner
All NRI photos are scanned with North to the top. The relationship of North to the film markings varies depending on: Flying direction. NRI photos can be flown North-South, South-North, East-West, or West-East. Type of camera The following slides will help you determine the proper orientation. All NRI photos need to be scanned with North oriented to the top regardless of the direction the photo was flown. Photo Characteristics

28 Top of the Scanner The front of the scanning bed is considered the top. Place the North end of the photo face down toward front of the scanner Place North Edge Here A Microtek 9800XL scanner with the Transparency Media Adapter (TMA). The North end of NRI photos should be aligned as shown above. Photo Characteristics

29 North Edge – Standard Title Block – Example 1
The NRI photography contract specifies that the photo is to be titled on the North edge. Standard Titling on North Edge What to scan? Scan the entire piece of film including the data strip and fiducial marks. Standard title block on North end of photo. Titling is a manual process and mistakes are occasionally made with the wrong end labeled North. The entire piece of film including the data strip and fiducial marks is to be scanned. Photo Characteristics

30 North Edge – Standard Title Block – Example 2
The NRI photography contract specifies that the photo is to be titled on the North edge. Notice that this photo has the data strip on the opposite end from the previous slide. Standard Titling on North Edge What to scan? Scan the entire piece of film including the data strip and fiducial marks. Standard title block on North end of photo. Titling is a manual process and mistakes are occasionally made with the wrong end labeled North. Photo Characteristics

31 North Edge – Automated Titling – Example 1
Automated titling varies. Look for the North arrow to determine the correct orientation. What to scan? Scan the entire piece of film including the data strip and fiducial marks. Automated titling varies by camera and vendor. Look for the North arrow to determine the correct orientation. Photo Characteristics

32 North Edge – Automated Titling – Example 2
Automated titling varies. Look for the North arrow to determine the correct orientation. What to scan? Scan the entire piece of film including the data strip and fiducial marks. Automated titling varies by camera and vendor. Look for the North arrow to determine the correct orientation. Photo Characteristics

33 North Edge – Automated Titling – Example 3
Automated titling varies. Look for the North arrow to determine the correct orientation. Notice this is actually a West arrow. The photo is oriented correctly with West to the left and North to the top. Automated titling varies by camera and vendor. Look for the North arrow to determine the correct orientation. What to scan? Scan the entire piece of film including the data strip and fiducial marks. Photo Characteristics

34 Use, Care and Storage of Aerial Photos
Proper Handling of Photographic Materials Cleaning Storing and Archiving Additional Notes

35 Proper Handling of Photographic Materials
Things you can do to protect your photographic materials… Keep your work environment and tools clean Wear lint-free gloves Keep photos in protective sleeves Store photos under the best possible conditions Have copies made if you plan to use them in the field Keep transparencies clean REMEMBER! The NRI photo transparency is the original film from the camera. No backup copies exist. If you have to ship an original NRI photo, use FedEx and declare a value Tips for proper handling of NRI photos. Remember that the photo is the original film from the camera. No other copies exist if a photo is lost or damaged. Photo Characteristics

36 Proper Handling of Photographic Materials
What can damage photographic materials? Fingerprints, dirt, dust, moisture, mold and prolonged exposure to lights can threaten their quality or worse, render them useless. Example of a fingerprint on a photo. Photo Characteristics

37 Cleaning and Repairing Photographic Materials
Acceptable Cleaning Materials Cotton Fabric White or light colored Anti-static cloths are ok as well Soft-Bristled Brushes Flat, camel’s hair Create a static charge by brushing the bristles over a plastic rod such as a pen Compressed Air Make sure the air is filtered to avoid sandblasting and oil spots Solvents Isopropyl alcohol—98% purity or higher!!! Ethyl alcohol—98% purity or higher!!! Tips for cleaning photos. Photo Characteristics

38 Cleaning Photographic Materials
Good ventilation and sufficient air flow Use soft, lint-free cleaning fabric (cotton) Test a discrete area before you begin Moisten, clean and re-moisten with solvent—DO NOT SATURATE YOUR PHOTOGRAPH! Clean one small area at a time Repeat if needed, but be conservative in your cleaning approach! Tips for cleaning photos. Photo Characteristics

39 Storing and Archiving Photographic Materials
Protect from light sources Use proper storage containers i.e., metal or archival grade safe boxes Do not stack or pack tightly to avoid pressure on your prints and negatives Interleave them with acid-free paper Use moisture-proof storage envelopes Control temperature and humidity Avoid storing them near heat sources or ozone-generating machines i.e., photocopiers Silica gel packets help to dehumidify Packing Materials Use proper storage containers i.e., metal or archival grade safe boxes Avoid using original packaging—it will break down over time and damage your photographic materials Storage Location Main or upper floors and at least 6 inches (15 cm) above the floor Protect against fire Fireproof storage vaults Fire cabinet or safe They must be able to prevent temperatures from rising above 100°F (38°C) Tips for storing photos. Photo Characteristics

40 Do not use markers to write on the film or protective sleeve!
Additional Notes Unlike unprocessed film, prints are not affected by x-rays i.e., airport security Do not store black and white and color negatives together in the same envelope Do not use markers to write on the film or protective sleeve! Do not mark on film or protective sleeve. Photo Characteristics

41 Summary Brief introduction to photo characteristics
Formats, film types, range of scales Footprints Photo Markings (title block, fiducials, focal length) Photo Geometry Scale varies with relief Radial displacement Photo Resolution Orientation for scanning Proper Storage


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