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Digital Aerial Imagery Calibration Range Requirements

EROS Remote Sensing Technology Project

September 2008

Version 0.2 DRAFT 4/7/2018 1.0 Scope...... 3 2.0 Overview...... 3 3.0 Range Implementation Requirements...... 4 3.1 Range Specifications...... 4 3.2 Ground Point Specifications...... 5 3.3 Spatial Target Specifications (Optional)...... 6 4.0 Range Maintenance Requirements...... 7 5.0 Range Usage Requirements...... 7 Appendix A: Figures and Tables...... 9 Appendix B: TBR/TBDs...... 13 Appendix C: Acronyms...... 14

2 Draft DRAFT 4/7/2018 1.0 Scope

This document defines the United States Geological Survey (USGS) requirements for building, maintaining, and using standardized In Situ Calibration Ranges (ISCRs) for the purpose of calibrating and/or validating aerial sensor systems. Calibration over these ranges is intended only to be geometric calibration, the determination of the systems interior orientation parameters including lens distortion or some subset thereof. The calibration can then range from a full, from-scratch calibration to the tweaking of a single, previously determined parameter. The ISCRs could also be used for such things as validation of geometric calibration and system response over time of aerial digital sensor systems and, in some limited circumstances, be used to support a boresight calibration.

The development of these ranges is directed primarily towards aerial camera system owners and manufacturers of flight-worthy digital cameras. Secondarily, the ISCRs are directed towards any other safe (i.e., non-injurious to plants and/or animals) sensor system and towards contracting officials who may require the calibration results from the primary users for assessment purposes.

Unless prior approval is given by the USGS, the results of an in situ calibration over one of these ranges would not be considered as a replacement of any prior calibration of an aerial camera system.

2.0 Overview

The ISCRs will be distributed throughout the United States to provide easy access for everyone. They will be uniform in ground coverage, rectangular (TBR-0) in shape, and oriented in a cardinal direction (i.e., either from north to south or from east to west). The rectangular shape will provide flexibility in the planning of flight lines for the disparate image footprints of the various aerial sensors to ensure an adequate number of images for a proper calibration.

The ranges will cover non-flat terrain, have precisely surveyed ground points, and have a Continually Operating Reference Station (CORS) readily accessible. The ground points will be either signalized control points for computing a calibration bundle solution or image identifiable/signalized check points to evaluate the “goodness” of the bundle solution. This will provide sufficient data for users to determine or validate, and the USGS to assess, the camera’s calibration.

In addition to these physical attributes, the ISCRs will have accessibility attributes such as open airspace, low air turbulence, no dangerous vertical obstructions, and convenient ground access to the range for routine maintenance. It is of primary importance that the users of the range have a convenient and safe environment to collect the data required for the determination or validation of the sensor’s calibration.

3 Draft DRAFT 4/7/2018 3.0 Range Implementation Requirements

There will be two co-resident ranges within each physical range; usually, one for larger format digital (and film mapping) cameras and one for smaller format cameras. Depending on the purpose of the over-flight and for flexibility, any camera system can be flown in either cardinal axis direction and in either of the two range layouts to produce four distinct range options. See Appendix A for Tables and Figures providing support for the requirements in this section.

3.1 Range Specifications

1) The extents of the ranges were derived from the characteristics of typical camera systems (Figure 3.1-1: Range Extents and Placement).

a) The larger range shall have a ground extent of 1750 (TBR-1) by 2000 (TBR-1) meters. b) The smaller range shall have a ground extent of 600 (TBR-1) by 750 (TBR-1) meters and be totally within the larger range.

2) The orientation of the longer dimension for all ranges shall be east/west or north/south.

3) The terrain variation within any range shall be at least 100 (TBR-2) meters (Figure 3.1-2: Terrain Variation Examples).

a) Terrain shall not be uniformly sloped over the range’s extent. b) The top of a stable manmade object may used in the determination of terrain variation if a control point is located on top of this object. c) The control point variation shall be at least 75 (TBR-2) meters.

4) The range area shall be within 40 km of a Continually Operating Reference Station (CORS) that operates at a minimum rate of five (TBR- 3) seconds (one second CORS is preferred).

5) Ranges should be located in areas that are predominately cloud-free.

6) Ranges shall be easy and safe to access.

a) Ranges shall not be located within 10 (TBR-4) kilometers of controlled or restricted airspace (including maneuvers to line up for flight lines). b) Ranges shall be located at least 10 (TBR-5) kilometers from obstacles over 100 meters in height. c) Ranges shall be located at least 15 (TBR-6) kilometers from any source of significant turbulence that is present and active during typical over-flight times.

4 Draft DRAFT 4/7/2018 3.2 Ground Point Specifications

1) Each range shall contain at least 50 (TBR-7) signalized control points.

a) Control points shall be surveyed to a minimum accuracy of 2 (TBR-8) centimeters at one sigma (i.e., standard deviation) horizontally and vertically. b) The range with the larger extent may share a subset of the points from the range with smaller extent. c) The points shall be uniformly, but randomly, distributed throughout the range such that no less than 20 percent of the points (rounded value) fall within any quadrant of the range (Figure 3.2-1: Point Distribution Constraints). d) No two control points shall fall closer than the square root of the following computation; range length times the range width divided by two and one half times the number of points (Figure 3.2-1: Point Distribution Constraints). e) Control points shall be intervisible to all image exposure stations falling within an inverted 45 (TBR-9) degree right circular cone with its apex at the control point (Figure 3.2-2: Control Point Intervisibility). f) Signalized control points (i.e., panels) shall have an acceptable shape and dimensions (Table 3.2-1: Acceptable Signalized Control). i) The surveyed location shall be at the precise center of the panel. ii) Painted panels on asphalt or concrete shall be constructed and centered on a surveyed nail, pipe, rod, spike, punchmark, drillhole, or other semi-permanent mark. iii) Panels constructed from other materials (such as sheets of material anchored to a roof) shall be centered over a similarly recoverable, semi-permanent surveyed point. iv) The white surfaces of the panels shall be painted with that specified by standard Diamond Vogel Paints Traffic Paint White Oilbase (TB- 1501) or equivalent. v) The black surfaces of the panels shall be painted with that specified by standard Diamond Vogel Paints Traffic Paint Black Oilbase (TB- 9502) or equivalent. vi) The placement and painting of panels shall conform to local laws/restrictions. g) Control point panels shall be located so as to allow for convenient maintenance.

2) Each range shall contain at least 25 (TBR-10) check points to be used to evaluate the calibration solution.

a) Check points shall have the same specifications as control points for accuracy, sharing, distribution, and intervisibility (1a-1e and 1g above).

5 Draft DRAFT 4/7/2018 b) Check points are not required to be signalized (i.e., permanently marked), but if signalized, they shall have the same specifications as control points. c) Once the check points have shown an independent verification of the goodness of a range over-flight, they may be used as extra control points for computational purposes.

3.3 Spatial Target Specifications (Optional)

The determination of relative edge response and image resolution will be somewhat limited due to the rather small size of the modified Siemens Star, henceforth known in this paragraph as the star, (Figure 3.3-1: Modified Siemens Star and Figure 3.3-2: Alternative Modified Siemens Star, henceforth known in this paragraph as the figures) being specified. The purpose of the modified star is to provide black to white edges at a controlled set of orientations such that a relative edge response can be obtained even when the images are not truly oriented to a cardinal direction.

1) The star shall be broken up into four quadrants. 2) The star shall be oriented to one of the four cardinal directions (i.e., north, east, south, or west). 3) The star shall have the same intervisibility constraints as for control points. 4) The spokes on the star shall be 3.2 (TBR-11) meters in length. 5) The distance between black areas in adjacent quadrants, except for the middle spokes in quadrants 1, 2, and 3 and all spokes in quadrant 4, shall have at least one (TBR-11) meter separation to provide sufficient room for the determination of relative edge response. 6) Three of the star’s quadrants (i.e., quadrants 1, 2, and 3 in the figures) shall have spokes with 18 (TBR-11) degree angles. 7) The spokes of that portion of the star in the fourth quadrant shall have angles of 10 (TBR-11) degrees. 8) The spokes in each quadrant shall have specific orientations to provide flexibility in the determination of relative edge response. a) Quadrants one and four shall have no rotation to the cardinal direction. b) Quadrant two shall be rotated four degrees clockwise to the cardinal direction. c) Quadrant three shall be rotated eight degrees counterclockwise to the cardinal direction. 9) The ends of the spokes shall have specific orientations (Table 3.3-1: Siemens Spoke End Orientations) to provide flexibility in the determination of relative edge response. 10) The white surfaces of the star shall be painted with TBD-1. 11) The black surfaces of the star shall be painted with TBD-1.

6 Draft DRAFT 4/7/2018 4.0 Range Maintenance Requirements

The USGS will develop cooperative agreements with groups from governmental bodies, industry, and academia (i.e., range sponsors) for joint planning and building of ISCRs. Once built, the sponsors will perform all maintenance on the range and USGS will assist the sponsors with any rework of the range.

1) All routine range maintenance and inspection shall be performed by the sponsor of the range. 2) The sponsor shall maintain a historical record of all inspections of the range and any maintenance performed on the range. 3) The sponsor and USGS shall determine the frequency, scope, and reporting of routine inspections. 4) The USGS shall provide a special maintenance request to the sponsor when users of the range report a control point recovery rate of 90 percent or less. 5) The USGS shall provide a maintenance advisory to the sponsor when the control point recovery rate goes below 95 percent or spatial calibration targets become difficult to use.

5.0 Range Usage Requirements

The primary use of the ISCRs is for geometric camera calibration which can be split into at least three levels: full calibration, parameter tweaking calibration, and calibration validation. Each of these levels requires varying range resources and varying collections of imagery. In some situations the range could be used for boresighting a camera system when the flying conditions (e.g., camera type and flying height) are appropriate. It will be up to the range user to determine how to best use the range for the user’s purposes.

1) The range user shall notify the USGS and the range sponsor of a planned over-flight. 2) The range user shall provide the USGS with a copy of the imagery used for calibration purposes and the results of the calibration. 3) At least 80% of the control and check points shall be imaged on two or more exposures for calibration purposes. 4) All control points that are imaged must be part of the calibration solution as control points. 5) Calibration results shall be in ASCII form and shall consist of: a) Derived calibration parameters with statistical measures and parameter correlation information. b) Mensuration data. c) Control point data. d) Exterior orientation data. e) Camera data.

7 Draft DRAFT 4/7/2018 6) The range sponsor shall inspect that portion of the range based upon and prior to the planned over-flight if within 5 (TBR-12) days of a routine inspection.

8 Draft DRAFT 4/7/2018

Appendix A: Figures and Tables

Examples of Valid Range Layouts s r e t e m

0 s s 5 r r e 7 e t t e e s r m m e

600 meters e 5 0 Non-Valid Range Layout m 7 0

2 1 0 0 6 750 meters s 2000 meters r e t

1750 meters e m

s 0 r 5

Cardinal Direction e t 7 e m

600 meters 0 0 0 2 s r e t e m

0 s r 0 s s e 6 r r t e e e t 1750 meters t e e

750 meters m

0 0 0 0 5 5 2 7 Cardinal Direction 7 1

600 meters

2000 meters 1750 meters

Figure 3.1-1: Range Extents and Placement

Valid Range Terrain Variation Non-Valid Range Terrain Variation (Insufficient Terrain Variation)

106 meters 106 meters

Terrain profile through minimum and maximum Nominal terrain profile throughout the range elevation across limits of range. Profiles parallel and which is normal to direction of slope. to this profile have variability.

Figure 3.1-2: Terrain Variation Examples

Distribution for 20 point case Spacing (80% of 25 evaluation points) Dx

>20% >20%

>20% >20% Dp

1/2 Dp (min) = (Dx x Dy / 2.5 N)

Dp (min) = 265m ; where Dx = 1750m, Dy = 2000m, and N = 20

Dp (diagram) ~ 290m

Figure 3.2-1: Point Distribution Constraints

Valid Intervisibility Non-valid Intervisibility

Normal to Ellipsoid

Control/Evaluation Point Building (or tree, etc)

Figure 3.2-2: Control Point Intervisibility

8 degrees from cardinal Cardinal direction 1 2 4 degrees from cardinal W

8 degrees from cardinal B B 1m 4 degrees from cardinal B 1 3 B 2 2

3.2m B 3 1 B W Cardinal direction 4 degrees from cardinal 8 degrees from cardinal 8 degrees from cardinal B W Cardinal direction 1 B B Legend 2 B - Black 3 B W - White B n - Quadrant # B B 12 degrees from cardinal n - Spoke # B B

Cardinal direction

Figure 3.3-1: Modified Siemens Star

3 4 W W

B B B B

B B B B B B

W 2 1 W

Legend B - Black W - White n - Quadrant #

Figure 3.3-2: Alternative Modified Siemens Star

Bullseye Plus or X TBD-2 a white black w

h c i t 1.5a e b white a 2a 4a black black white

Range Minimum Size (cm) Maximum Size (cm)

Type a b c a b c

Larger Format 20 52 16 30 78 24

Smaller Format 14 34 10 21 53 16

Table 3.2-1: Acceptable Signalized Control

Quadrant Number 1 2 3 Spoke Number 1 3 1 3 1 3 Rotation Angle from Cardinal (deg) 4 CCW 8 CW 4 CCW 8 CW 12 CCW 12 CW

Table 3.3-1: Siemens Spoke End Orientations

12 Draft DRAFT 4/7/2018 Appendix B: TBR/TBDs

TBR/TBD # Paragraph # # of References Point Needing Clarificatuion Work-off Date TBR-0 Overview 1 Rectangular shape of the ranges TBR-1 3.1 4 Ground extents of the two ranges TBR-2 3.1 2 Minimum terrain and control point variation TBR-3 3.1 1 Operational rate of CORS TBR-4 3.1 1 Distance from controlled or restricted airspace TBR-5 3.1 1 Distance from vertical obstructions TBR-6 3.1 1 Distance from areas of usual and excessive turbulence TBR-7 3.2 1 Number of signalized control points per range TBR-8 3.2 1 Accuracy of the signalized control and check points TBR-9 3.2 1 Intervisibility angle for control and check points TBR-10 3.2 1 Number of check points per range TBR-11 3.3 4 Dimensions on modified Siemens star TBR-12 5.0 1 Advanced inspections of range for overflights TBD-1 3.3 2 Specification for white and black paint TBD-2 Table 3.2-1 1 Name for shown signalized control point

13 Draft DRAFT 4/7/2018 Appendix C: Acronyms

Acronym Name CCW CounterClockWise CORS Continually Operating Reference Station CW ClockWise ISCR In Situ Calibration Range TBD To Be Determined TBR To Be Resolved USGS United States Geological Survey

14 Draft