3. Review of Equipment

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3.1 Video Camera Systems

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In the last 10 years there has been an exponential increase in the type and availability of video equipment. The choice of equipment which is best suited for a particular AVI survey depends largely on the intended use of the images and budget limitations. Successful surveys have been completed using most of the available systems. The following discussion provides a summary of video systems, and their applicability to survey requirements.

The tables of equipment are organized in a descending order of quality (see Table 3). This list is a general guide to cameras and recorder types. The ever increasing availability of equipment in the professional, industrial, and consumer markets may shift the desirability of individual formats. For example, Sony has recently announced the release of "Prosumer" digital recording systems. It must also be recognized that equipment should be evaluated on an individual basis, as features vary widely between equipment. A more detailed evaluation of individual camera/recorder features is included in Appendix D.

The recent shift in technology have made the use of tube cameras in the field less desirable. Most modern electronic news gathering (ENG) video systems are based on some form of charged-coupled diode (CCD) technology. These are the best systems to use in a field environment due predominantly to their size and durability. This is also true for most consumer camcorders. Tube cameras, especially three tube colour systems, are susceptible to shock and image burn on bright objects. This causes considerable difficulty on aerial surveys, where sun glare off the water is a concern, and aircraft vibration a constant. They are included in this review as there is a large number of these systems still available in the rental/lease market. Their use has generally shifted to the studio or fixed position environment.

Quality of Image

The quality of the image, also commonly referred to as camera resolution, is dependent on two factors. The quality of the lenses and the capability of the pickup device to convert the "light image" to an electronic signal. The quality of lenses is a basic concept and is analogous to the differences of an inexpensive point and shoot camera to a high quality 4x5" format camera. One of the most important factors in lenses, especially in the consumer market, is their composition, plastic or glass. Glass lenses traditionally provide better light transmission and convergence properties. The conversion of the image in the camera is performed by the video tube or CCD. Three tube or chip cameras generally use one chip for each of the three primary colours, and electronically mix the results. Single tube or chip cameras use only a single composite colour device. A combination of pixel density, size of the device and number of devices will make up the final image resolution. Generally cameras with larger pickup devices and/or more devices will have a higher resolution. Multiple variations in these designs are available from different manufactures, and comparisons should be made on the specifications of each system individually.

It is important to be aware of the difference between the camera resolution and the recorder resolution. The camera resolution as discussed is the output capability of the camera. This should not be confused with the resolution of the final image on the recorded videotape. This is especially true of camcorder systems where the camera and recorder are combined. The final quality on videotape is dependent on the capability of the recorder as well as the camera. As a general rule the camera should be capable of producing "more" image than the recorder can reproduce as other factors such as the signal to noise ratio play an important part in the final result. Systems should, however be reasonably matched. For example using a professional 700 line camera on a standard VHS recorder which is capable of recording only 230 lines of information will result in a recording at only 230 lines.

Camera Features

A considerable variety of features are available on camera systems. Many of theses features are important to the usefulness of the camera and others provide varying degrees of convenience. Following is a brief discussion of the features which should be considered for aerial videotape surveys.


3.2 Video Recording Systems

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Most of the video formats are available in both separate camera/recorder systems as well as varying combination of camcorders (Table 4). A separate camera/recorder system is preferable for aerial video surveys as these systems usually provide better recording features and flexibility. This type of configuration, for example, would be best suited for connection of GPS encoders. Camcorders are however usually less expensive. Considerations of quality versus cost, availability and compatibility are trade-offs. A Betacam system can exceed $20,000, whereas a standard 8mm camcorder costs under $1000. Rental and/or lease costs will vary proportionally. When making the decision of which system to use for a survey keep in mind that the price of the camera system is generally a small part of the survey costs, especially if using a helicopter.

For the purpose of this review the term "recorder" refers to both separate recorders and the recording part of camcorder systems.

Considerations must also be made for the timely use of videotapes after each survey. If an immediate analysis of the imagery is required, a duplicate system may be necessary in the office, which will increase costs. If there is time to make copies for distribution, the highest quality (on the initial recording) possible will result in less generation loss in copies, and imagery can be copied to other more compatible formats. If information response timing is important, remote transmission and satellite bounce systems are also available, at a cost!

Recorder Quality

The quality of the image which a video tape recorder (VTR) records is dependent on the method of magnetic storage, a combination of frequency deviation, band width, carrier frequency, colour separation and luminance signals. The technical aspects of this are not important for this discussion; however, an understanding that different formats will provide varying results is. The measure of quality is again that of horizontal lines of resolution. These are not to be confused with the horizontal scanning lines (512) on a standard North American TV (NTSC). The lines of resolution in cameras and recorders refers to a measure of individual lines which can be separately resolved by the human eye, or more simply the detail which can be observed in the image. Standard broadcast TV and most standard TV sets are capable of reproducing only 230 lines of resolution. This is the reason that the original VHS standard was set at this level. More recent TV/monitors in the market place are capable of reproducing 600+ lines.

It is important to match the components of the system to take the advantage of their capabilities. A Betacam recorder played back on a standard TV will not take advantage of the level of information available.

Tape Size and Specifications

The different formats not only have varying degrees of quality but differ in the size and nature of the recording tape. The 3/4 inch Umatic systems use large cassette tapes about the size of a good computer reference manual. The Hi8 and 8mm cassettes are close the same size as an audio cassette tape. The VHS and Betacam tapes are closer to pocket book size. In general the larger the videotape the larger the recorder. This aspect should be considered when choosing a field system. Small components are better if you have a tight recording platform. The smaller videotapes are also easier to store. This is especially important if the information is valuable and needs to be stored in a fire proof vault. Recorder size is also influenced by the number and type of features the system has. Small "palm-corders" have fewer features than full size recording decks of equal quality.

The different tape formats also support varying numbers of recordable channels beyond the basic video imagery (Fig. 1). These channels could include the audio, time code, control track, index, data and/or date stamp. For example Hi8 videotape supports two separate stereo recording channels. The AFM channels are recorded along with the video signal in the helical scan and two PCM digital audio channels are recorded on linear tracks along the tape. Betacam provides up to four linear tracks, 3/4 inch two linear tracks and SVHS provides one separable stereo track (left and right) as well as a mono dub track. Hi8 and 8mm videotape supports a timecode track, 3/4 inch Umatic only supports a control track, and VHS only records index marks. The access to these features depends on the support provided by the individual recorder system. It is important to review the specific requirements of the survey and post survey analysis to determine what features are important.

Figure 1 Typical videotape recording layout

Recorder Features

A considerable variety of features are available on recorder systems. Many of theses features are important to the usefulness of the system and others provide varying degrees of convenience. The following is a brief discussion of the features which should be considered for aerial videotape surveys.


3.3 Communications Systems

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The inclusion of an audio commentary on the videotape is one of the simplest techniques to add value to a final product. It is, however, the one option commonly omitted from aerial surveys. Detailed features (e.g., substrate types, species occurrence) may be easily identified by experienced observers during the overflight, but may not be discernible on the imagery. As a minimum, a good quality microphone should be used, but a proper aircraft, voice-activated, headphone/microphone communication system is preferable; the use of voice-activated microphones leaves hands free for other onboard functions such as taking photographs or camera operation.

Consideration must also be made for the intended use of the video imagery. For example, a single channel system is appropriate if only shore zone morphology is important but a two channel system is required if both physical and biological descriptions are desired. The communication system also provides for interactive communication between all members of the survey team, including the pilot. All topics discussed and information described is recorded onto the videotape. This could include not only shore-zone data, but location information, altitude, air speed and any other general information which any member of the team felt was important.

Table 5 summarizes the common options for videotape commentary systems.

Positioning Systems

One of the most important aspects of AVI surveys is the ability to locate a particular section of video imagery on a map. With the current satellite network and importance of linking all electronic data into compatible systems, the use of GPS is becoming an advantageous approach.

The Global Positioning System (GPS) is not a new technology, having been available for over 20 years. The use of these systems for AVI surveys has only been viable for the last few years due to the incomplete coverage of the satellite network. As recently as 1989 the satellite coverage over North America was not sufficient to use GPS as a navigation option during shoreline over flights for the Exxon Valdez oil spill.

General GPS Description

A general description of GPS is excepted from the U.S. Federal Navigation Plan GPS Statement:

GPS Receivers

GPS receivers are available from a number of manufactures and in many different formats, capabilities and features. Prices range from under $400.00 US to over $60,000; the units that have the capabilities required for AVI surveys are in the US $1000 to $3000 dollar range.

Major features about a GPS to consider are:

Linking GPS Data to the Video Imagery

When examining the use of GPS in AVI surveys there are four main alternatives for linking GPS data to video imagery:

Each of the GPS data and audio commentary options is diagrammed below, and discussed with their respective advantages and disadvantages.

Figure 2 Schematic diagram of procedure for "burning" GPS to the video image or recording GPS to the close-captioned video track (Techniques 1 & 2)

Data to Video Converter:

Audio:

Video:

GPS Receiver:

Advantages:

Disadvantages:

Video burn in does not allow computer access of the data off the tape for further processing. The data would also have to be independently recorded on a laptop computer or other data recorder and linked to the imagery via a time code; this step requires planning to assure time code on tape and computer are synchronized.

Figure 3 Schematic diagram of procedure for recording GPS data to an audio sound track on the video tape (Technique 3)

Data to Audio Converter:

Audio:

Video:

GPS Receiver:

Advantages:

Disadvantages:

Figure 4 Schematic diagram of procedure for recording GPS data to a laptop/ datalogger (Technique 4)

Audio:

Video:

GPS Receiver:

GPS Data:

Advantages:

Disadvantages:


3.4 Aircraft

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The use of different platforms for video surveys depends on a good understanding of the survey objectives. A fixed wing aircraft may be adequate if a regional overview is all that is required. For detailed shore zone analysis it is necessary to fly at lower altitudes and therefore much slower than is capable from most fixed wing aircraft. Selection of the appropriate aircraft requires an understanding of the relationship between flight altitude, flight speed, aircraft type and camera capabilities. The following discussion provides a general overview of fixed-wing and helicopter platforms.

Some aerial video survey systems are permanently mounted in aircraft whereas other approaches use chartered aircraft near the survey site. Some advantages of using dedicated aircraft include: little set-up time, avoidance of electrical/radio noise problems, permanently installed GPS antennas and ergonomically-laced controls for easy operation. The major disadvantage of using dedicated aircraft for AVI is the cost of aircraft ferry time to and from the survey site; small surveys at distance from the aircraft base become expensive.

Fixed Wing

Fixed-wing flying platforms have been widely used for AVI surveys and, with proper attention to details, can be used for reconnaissance and interpretative-type surveys. In general, the following features are desirable:

There are special considerations for the use of fixed-wing capabilities. If the camera is an externally-mounted camera, windows are not a problem; externally mounted equipment is subject to MOT approval, however. There are specially modified aircraft with floor ports for vertically-mounted camera systems, negating the need for opening or removable windows. One commercial video service (see Project Summary No. 4 in Appendix B) has a specially-designed Plexiglas pod in bottom of the tail-boom to allow an internally-mounted camera with wide pan and tilt capabilities.

Fixed-Wing Advantages

Fixed-Wing Disadvantages

Helicopters

Helicopters have also be used extensively for AVI surveys in the Province. The superior maneuverability provides for a more flexible camera platform and their ability to land, means that surveys can be interrupted to ground-truth ambiguous features. The main features to consider in helicopter selection are:

Advantages of Helicopters

Disadvantages of Helicopters

In summary, the major advantage of a helicopter of a fixed-wing aircraft is in speed and maneuverability but this advantage comes at 3-4 times the cost. If the primary survey objective is a more regional overview and the features of interest are primary linear, fixed-wing surveys would provide a more cost effective approach; however, if details are required, such as species identification, and the features of interest are crenulated, then a helicopter-based survey may be the only appropriate approach.


3.5 Special Equipment

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Computer Access Systems

The increased importance of computer databases in environmental resource inventories and contingency response planning makes videotape an ideal medium for information gathering and storage. Moderately priced video playback units can be directly controlled by common desktop computer systems allowing simultaneous access to data and playback of the aerial videotape imagery. If faster response than can be provided by videotape is required, the imagery can be transferred to laser disk for direct access. This level of information presentation is fast becoming a required industry and government standard, where text, maps, visual imagery and audio descriptions are linked in an easy-to-use system. The power of small database computer systems has made the use of geographical information systems (GIS) common place (e.g., QuikMap, MapInfo, ArcView). Most systems will allow the incorporation of still pictures into the database. By adding direct access video, a still picture (freeze frame) can be accessed anywhere on the tape, taking advantage of the consistency and continuity of the media.


3.6 Approaches for Meeting Survey Objectives

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This section provides an overview of alternatives for achieving a variety of survey objectives using various equipment components and survey platforms. Specific survey scenarios are outlined and alternatives approaches for meeting objectives are listed (Table 6). A discussion of each of the scenarios is provided.

Scenario 1 - Overview for Log-Dump and Stream Crossing Siting

An overview of site conditions are required for preliminary screening of the area. No previous information is available other than 1:50,000 scale topo maps, 1:80,000 scale charts and 1:20,000 air photos. The survey should document general conditions in a 2-3km section of coast and 1 km inland along a small stream. The survey should be conducted at low-tide as intertidal areas will be impacted by the log-dump. The data will serve as a preliminary basis for additional surveys and planning by the project team.

Chartering of a locally-based, fixed-wing floatplane is dictated by the short duration of the survey. Consumer-grade Hi8 or SVHS hand-held recording equipment is appropriate as this equipment is easily available but provides a higher quality than conventional VHS or 8mm video. In that a relatively small area will be covered, recording flightlines on a blown-up copy of 1:50,000 scale topographic map is an appropriate documentation as imagery will have very limited distribution. Video imaging by the operations manager is appropriate as he is familiar with the information that will be needed in future planning.

Scenario 2 - Overview of Washout and Slope Failures

The purpose of the survey is to inventory stream washouts and local slope failure in a Special Area watershed as a result of an exceptional rainfall. The emphasis of the survey is to concentrate on problem areas, rather than a systematic inventory of the entire watershed. Good quality imagery is required to serve as a basis for mitigative actions and potentially for litigation. Good positioning is required so that problem areas can be precisely located.

Again, because the survey is of limited duration, chartering of a local fixed-wing aircraft is most appropriate; however if on-the-ground inspections are necessary, a helicopter may be required. High quality, consumer-grade video equipment is appropriate as it is available locally and easy to use. A detailed airphoto (1:10,000 scale) could be used to locate failures or alternatively a hand-held GPS used to locate the site and position added to the narration. A stream hydrologist or slope stability specialist is the most appropriate individual to be imaging as they can provide an inflight commentary and know most critical features to document in the imagery.

Scenario 3 - Shore-Structure Survey

The Lands Department requires a detailed, synoptic record of shore structures located within the regional land district. The purpose of the survey is to document un-permitted structures in the foreshore. The region contains about 2,000 km of shoreline. Low tide surveys are not required so the time of the survey is not constrained.

A fixed wing aircraft with an external pan-tilt camera mount is probably appropriate due to the length of the survey - an estimated 15 hours of survey time. A fixed wing aircraft offers extended flight time between refueling stops and ergonomically-positioned controls to permit extended surveys (est. 5 hours of survey per day). Professional quality Hi8 or SVHS systems are recommended to facilitate GPS burn-in and synchronous GPS data recording on the audio tracks. A GPS burn-in system is recommended because of the potential use of the imagery in litigation, and a GPS recording system is recommended to facilitate flightline plotting and data management. A near-vertical imaging mode should be sufficient to resolve shore structures. The camera system would be operated by a technician and the land manager would accompany the flight as a client observer.

Scenario 4 - Shoreline Survey for Oil Spill Planning

This data is required for interpretative purposes and to develop oil spill sensitivity maps. In particular, intertidal sediment size determines potential residence of stranded oil and biological zonation contributes to sensitivity. Because it is not possible to resolve the sediment size characteristics or intertidal biota from the imagery alone, specialist narrations and 35mm photos provide important supplementary data. Surveys must be conducted at low tide only so are limited to a 3hr/day tide window.

A helicopter survey platform is recommended to increase maneuverability along the highly crenulated coast and to provide low-altitude (100m), slow-speed (<100km/hr) overflights. A hand-held camera system is recommended because the aircraft undergoes considerable attitude variations while flying along the crenulated coast. The professional quality Hi8 or SVHS system is recommended to provide dual channel audio-recording capability and to provide GPS burn-in capability; the GPS burn-in is recommended as tapes are likely to be used by a wide range of agencies and the positioning data is then permanently linked to the imagery. GPS data will be continually recorded to facilitate flight line recording and data management.

Scenario 5 - Stream Habitat Characterization

A standard aquatic habitat inventory program requires stream habitat characterization mapping to 1:20,000 scale maps. Stream courses are highly sinuous and terrain very steep. Inventory data provides the most detailed record of habitat so positioning critical.

Because of the sinuous nature of the streams and the steep terrain, a helicopter is recommended. The stream inventory program requires inventory of both banks of the stream as well as the stream channel; to avoid "shadowing" problems that occur with oblique, hand-held video, the use of a near vertical pan-tilt camera system is recommended. GPS data is logged to a lap-top computer for post-survey differential correction to DGPS standard as detailed positioning is required; DGPS data is linked to the video-imagery through the burned-in time code on the video image. Standard DGPS flightline files are maintained and the flightlines can be easily imported into GIS systems for data management purposes.

Scenario 6 - Estuarine Habitat Mapping

An inventory program of estuary habitat types requires planimetric mapping at 1:5,000 scale mapping. Planimetric video imaging was chosen over vertical aerial photography because of the limited duration of the survey and the need to fly during early morning, low tide windows (i.e., less weather dependency).

A vertical format video image is required to facilitate mapping so a fix mounted system is recommended. Resolution requirements of the mapping program will dictate the need for inertial navigation systems in the aircraft. Professional video equipment is recommended to allow time code to be recorded and linked to GPS datafiles on the laptop. Post-survey processing of GPS to DGPS recommended to improve location information to <5m accuracy. Screen captures of individual video frames will provide the basis for mapping within a desktop GIS system. Some ground-truthing required to verify aerial mapping interpretation.

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