Pros And Cons Of Different Platforms

This chapter has introduced a variety of platforms with different characteristics, all of which have been used by the authors in their work; even more can be found in the literature. A basic distinction between all platforms is the question of tethering or free-flying. Tethered platforms inherently have a lower operating space but are easier to position over fixed points. Free-flying aircraft may cover larger areas and distances but, with the exception of hovering types such as helicopters and multicopters, tend to cross over small areas of interests in the wink of an eye. Autopiloted systems and flightpath planning prior to a survey or live-view transmission systems are therefore highly recommended for such platforms.

The choice of possible platforms for an SFAP project is huge and continues to grow. It is difficult to generalize about advantages or disadvantages for particular platforms, because possible applications and working conditions vary greatly around the world. Cost of equipment and availability of trained personnel must be considered along with necessary logistical support, transport issues, and legal aspects associated with various types of platforms in different countries.

Nonetheless, it is clear that certain platforms would have desirable characteristics for conducting SFAP under particular circumstances, and what might be the ideal SFAP platform in one situation could be ineffective, impractical, or impossible in another. The decision for a particular one depends on numerous aspects which are always specific to the financial means, the technical skills of the personnel, the study area location and size, the required image characteristics, etc. Table 8-1 is an attempt of a more-or-less

TABLE 8-1 Comparison of selected platforms commonly used for SFAP based on authors' experiences and literature reports.

SFAP comparison

Platform cost

Operating energy

Operating cost

Transportability

Personnel

Risk

Wind

Flying height

Payload

Technical level

Positional precision

Are a I coverage

Stereo coverage

Vertical imaging

Exposure time range

Manned LSA

aviation fuel

«»••o

• 0

1-2

«••»0

calm to moderate

1000+ m

10 to 50 kg

• •••o

• •O

• ••••

• ••••

• ••

• •O

Helium blimp

• •0

helium

• •0

• •o

2

• o

calm to light

300+ m

5 to 10 kg

• O

• ••••

• ••o

• ••O

Hot-air biimp

• «•«0

propane

• 00

4+

• • 0

calm

300+ m

5 to 10 kg

• «•O

• ••••

• «•O

• ••O

• ••••

• ••••

Kite

• O

wind only

O

1-4

• o

light to strong

300+ m

<1 to 3 kg

• o

• •••o

• •O

• •o

• •O

• •O

Basic model airplane

• O

rechargable battery

• o

• •••

1-2

• o

calm to light

300+ m

VI

• •o

• ••o

• •O

• •o

Autoplloted airplane

rechargable battery

• o

• •••

1-2

• oo

calm to moderate

1000 m

<2 kg

• ••

Powered paraglider

• ••0

two-stroke gas mix

• oo

• ••0

2-3

• ••o

calm to light

1000 m

<2 kg

• ••o

• ••o

• ••o

• •O

• •o

Model helicopter

battery or gas mix

• oo

• ••0

1-3

«••0

calm to light

300+ m

<1 to 20 kg

See text for details of the individual aspects and parameters. Qualitative estimates: five solid dots, highest or best (relative to other platforms); open dots, variable, or uncertain rating. Maximum flying-height regulations vary from country to country and may be more restrictive in some countries.

subjective comparison looking at different parameters and characteristics, resulting from the authors' own experience and assessment combined with reports from colleagues and literature. The following considerations accompany the individual aspects.

• Platform cost: including all accessories except camera rig and camera.

• Operating energy and costs: electricity, fuel, lifting gas, or other energy sources necessary for platform power, camera, and other equipment.

• Transportability: is a function of equipment weight, storage space, and required transport means.

• Personnel: minimum number ranges from a single person to more than half a dozen people, as a result from different requirements depending on platform operation and mission objectives.

• Risk for personnel: a rough assessment of the risks the platform may present to the personnel (and onlookers) in case of malfunctions, forced landings, crash, etc. Ranging from no risk, to light and serious injuries, to danger of death.

• Wind conditions: approximate range of wind velocities in which the platform may be used safely.

• Flying heights: approximate realistic flying height at which the platform may be used safely and which may be subject to legal restrictions.

• Payload: includes camera, rig, ancillary equipment, and suspension; the ranges result from different carrying capacities depending on the platform size.

• Technical sophistication: degree of high-tech components, which may require specialized training to operate, and which could be difficult to adjust or repair in the field.

• Positioning precision: refers to the capability for positioning the camera exactly over a given ground target for vertical shots or with a specific look direction and tilt angle for oblique views.

• Areal coverage: refers to the ability to cover larger areas with gapless, contiguous vertical images.

• Stereoscopic coverage: refers to the ease with which stereopairs with photogrammetrically useful overlaps, exposure angles, and scale similarity may be acquired; in combination with the two preceding parameters for judging the possibility of acquiring individual stereo-pairs or larger stereoblocks.

• Vertical images: reliability with which a vertical image (<3° tilt) may be acquired.

• Exposure times range: depends on the platform velocity and vibrations. Low ranges mean short exposure times (< 1/1000) are required, larger ranges mean longer exposure times (e.g., 1/125) are also tolerated.

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