4. Recommendations of Survey Standards

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4.1 Factors Affecting Survey Quality

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A wide variety of aerial video imaging (AVI) is being conducted in British Columbia. Applications include: coastal resource inventories, fisheries habitat mapping for both coastal and river systems, shellfish habitat inventories, landscape feature mapping for use in forest cut-block planning and charting shoreline positions for hydrographic chart preparation. The wide range of applications has resulted in a wide variety of AVI platforms and collection techniques being used, with little standardization.

The flexibility of AVI has resulted in the independent development of numerous survey techniques. These range from the simple acquisition of oblique aerial imagery collected on an ad hoc reconnaissance basis with consumer-grade equipment to sophisticated systems using differential GPS (DGPS) positioning and inertial navigation systems. A single standard for AVI collection was not appropriate because of the wide range of survey objectives.

Table 7 provides a summary of user-controllable factors that control the overall quality of the AVI survey results. The table lists the various factors that influence the quality of imagery and associated interpretive value of the flight data. Users can evaluate various trade-offs between quality and cost in terms of their survey objectives.

4.2 Recommended Standards Criteria

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It is not possible to simply combine all the factors listed in Table 7 into a simple standard. Survey quality will also be affected by weather conditions during the overflight; for example, turbulence can affect aircraft stability, precipitation may degrade the image and bright sunlight may cause reflection problems off water surfaces. The recommended standards are based on the actual quality of the imagery and associated data rather than the intended quality.

Four key components of the survey data were selected for standardization:

· resolution, which is a function of the scale of the imagery (i.e., altitude and camera focal length), equipment resolution, aircraft stability and ground speed of the aircraft

· positioning, which presently range from rudimentary flightline maps to DGPS with inertial navigation systems.

· documentation, which varies from simple data sheets to comprehensive reporting.

· supplemental data, which can include: synchronous photography which is of a higher resolution than the imagery, synchronous narrative descriptions of features in the image that may not be resolvable in the imagery and synchronously recorded databases that involve data logged onboard during the overflight.

Table 7 Factors Affecting Aerial Video Imaging Survey Quality

		Survey Variables
Survey Quality	Cost	Camera	Recorder	Communications	Positioning	Aircraft	Inflight Interpretation	Data Logger
low	low	CCD, 1 composite chip or tube*	VHS	none	manual reconstruction of flightline	low-wing	none	none
ê	ê		8mm	single channel, mic	inflight 1 min fix marks	high wing, struts
ê	ê				GPS w video burn-in	high-wing, strutless	single, on-board interpreter
ê	ê	CCD, 2 chip or 2 tube*	SVHS		GPS w burn-in and logging	high-wing, strutless, STOL
ê	ê		Hi8		DGPS
ê	ê		3/4"Umatic		GPS w on-board GIS			on-board computer
high	high	CCD, 3 chip or 3 tube*	Betacam	multi-channel; voice-activated mic's	DGPS & inertial navigation	helicopter	multiple, on-board interpreters	on-board computer w GIS

*chips less shock & light "burn" sensitive than tubes

Image Resolution

For the purposes of this discussion, image resolution is defined as:

the smallest, consistently resolvable feature on the imagery, usually defined on the basis of a natural feature, such as a cobble or boulder.

This standard essentially addresses the composite affect of camera, recorder, aircraft speed and stability that affect image quality. Slow, low altitude overflights using a hand-held, consumer-grade cam-corder may have the same image resolution of a faster, higher overflight with professional-grade camera and recorder systems.

Positioning

Positioning is a critical component of AVI surveys in that there are often few distinct landscape features that can be used to reference the imagery. The advent of inexpensive, widely available GPS systems, which provide geographic positions within _100m of the true position, puts positioning within reach of all users. For the purposes of this project, we define positioning as:

the ability to relocate imagery in terms of a geographic coordinate system such as UTM coordinates or latitude and longitude.

Prior to the use of GPS, detailed flightline maps with frequent fixes were used to locate imagery; this process required an intermediate interpretation of an experienced navigator and is partially dependent of the scale of the maps used to plot the flight line. Many surveys have no or rudimentary flightline positioning, making the imagery difficult to locate for all but the original, inflight personnel.

Documentation

There is no standard of documentation for aerial video surveys. Often only a single version of flightline maps are available from the original project investigator, if at all, and there is no centralized repository of aerial video information. For the purposes of defining an AVI standard, we define documentation as:

supporting written, map or electronic information that documents the date and time of overflights, the survey coordinator, survey objectives, flight data (such as speed and altitude), geographic extent of survey, flightlines (either as maps or files) and standards (resolution, positioning, documentation and supplemental data standards as defined in this report)

A minimum documentation could be in the form of a data sheet, archived by a designated AVI coordinating agency and cross-referenced by NTS sheets. A more formal documentation might include a survey report and associated data files of the flightline.

The advantage of establishing a central clearing house for the aerial video survey data, is that some type of copying system could be established for the videotapes. At the present time, tape copies are obtained on a completely informal basis, and there is no quality control.

In view of the substantial, albeit dispersed, annual expenditure on aerial video surveys, the documentation needs improvement and a central clearing house should facilitate distribution.

Supplemental Data

Supplemental data collected during the overflight may greatly enhance the use of the imagery. For example, specialist commentary is critical to identifying features that may not be visible on the imagery but are visible during the survey (e.g., species distribution). Another example is where data may be logged directly into a laptop computer during the overflight. Supplemental data is:

information other than the imagery itself that enhances the interpretations that can be made from the video survey data.

It is our own experience and that of other users of AVI that the value of the imagery is considerably enhanced by having the end-user or interpreter (e.g., the stream hydrologist that will be classifying the stream habitats) in the aircraft providing a synchronous commentary, concentrating on features that may be marginally discernible on the imagery. In our coastal surveys (see Section 5, References), the coastal geomorphologist operates the camera at the same time as providing an inflight commentary; the commentary focuses on beach sediment composition, which is often difficult to resolve on the imagery.

4.3 Recommended Classification of Standards Criteria

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Because of the extremely wide range of survey objectives (i.e., reconnaissance, inventory and mapping) addressed by AVI surveys, we recommend that AVI be classified in terms of the four above-outlined criteria, rather than specifying standards (Table 8). Details of the ratings are summarized in Table 9.

It is envisaged that the imagery classification will be included on AVI datasheet (see next section) that catalogs basic information of the survey (e.g., location, custodial agency, contact, date, survey objective, etc) would include a classification designation (Table 10). The AVI classification will be included in associated documentation and labeled on the videotapes.

Table 8 Summary AVI Classification Standard

7

Order	Criteria	Rating
1st	Resolution	1 = highest resolution (<0.5m2) 2 = moderate resolution(0.5-2m2) 3 = lower resolution(>2m2)
	Positioning	1 = GPS or better (DGPS) 2 = <1:50,000 flightline maps 3 = >1:50,000 flightline maps
2nd	Documentation	1 = detailed survey report 2 = survey report 3 = data sheets on survey
	Supplemental data	1 = extensive supplemental data 2 = some supplemental data 3 = no supplemental data

Table 9 Explanation of Rating Criteria for AVI Survey Classification

Table 10 Example of AVI Classification of West Coast Shoreline Surveys

Survey	Resolution	Positioning	Documentation	Supplemental
Barkely Sound (1983)	2	2	2	2
Barkely Sound (1986)	3	3	3	2
Claoquot Sound (1993)	1	2	1	1
Nootka Sound (1994)	1	2	1	1
Johnstone Strait (1995)	1	1	1	1

Until such time as a lead agency is designated for AVI data, it is recommended that project managers be responsible for (a) classification of imagery and (b) submission of project data sheet to the coordination agency.

4.4 Other Recommendations

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There is a great deal of aerial video imagery available in the Province but sources are very difficult to locate, documentation is almost non-existent and tapes are filed on an helter-skelter basis. Some centralization would address these problems.

1. It is recommended that initially a Provincial agency be designated to maintain data sheets on AVI surveys. This coordinating agency would maintain a database of AVI surveys and small-scale location maps of flightline coverage within the province.

2. It is recommended that a standard datasheet be developed to summarize information on individual AVI surveys. A suggested format is provided in Table 11.

3. Should sufficient demand develop, videotapes could be archived with the coordinating agency to facilitate copying and distribution of the imagery

Table 11 Suggested Format for AVI Datasheet or Data Fields

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