High Altitude SFAP

According to Cohen and Small (1998), more than half of all humans live at elevations below 300 m, and nearly 90% live below 1000 m altitude. Thus, it is no surprise that most SFAP has been undertaken at relatively low altitudes. Chorier attempted kite aerial photography at 5600 m at Khardung La pass in the Jammu and Kashmir province of northern India, but was thwarted with strongly gusty wind and temperature of —15 °C. He did succeed nearby in the village of Khardung just below 4000 m altitude (Chorier and Mehta, 2007). This is the highest successful kite aerial photography known to the authors. In many high-mountain regions airfields even for small single-engine microlight aircraft are either not existent or not usable throughout the year. Using pilotless SFAP platforms, higher risks can be taken under difficult flight conditions.

For purpose of this discussion, high altitude is considered to be those regions above ~ 1000 m in elevation, and tremendous scientific interest exists for all types of environments at these high elevations. Global warming in high-mountain regions and related geomorphological changes provide a great challenge for SFAP. Glacier retreat and glaciofluvial geomorphodynamics in glacier forelands, erosion on moraines, development and outburst of proglacial lakes, changes in permafrost soils (patterned ground) due to permafrost-degradation, landslides, debris flows, and mountain floods are short-term processes whose spatial distribution and change dynamics are of highest interest in the near future. The same applies for vegetation impact by climate change, overgrazing, building operations, and winter-sports tourism.

The force that holds a winged aircraft up is determined by relative wind speed and air density acting on the lifting surface. At high altitude, lower air density means that fewer and lighter molecules (per air volume) flow over the lifting surface at a given wind speed. Air density is governed by three factors—pressure, temperature, and humidity. The combination of these factors determines potential lifting power of a particular winged platform for a given wind speed.

The standard atmosphere is an ideal model of atmospheric conditions (Table 9-1). These values reveal that density decrease is fairly slight up to about 1000 m high. At higher altitudes, however, air density declines significantly. At 3000 m, for example, air density is only about \ that of sea-level density. However, this assumes the standard atmospheric temperature of —4.5 °C at that altitude. At

TABLE 9-1 Standard atmospheric conditions for temperature, pressure, density, and density percentage according to altitude.

Altitude (m)

Temp. (°G)

Pressure (hPa)

Density (kg/m3)

Percent

Sea level

15.0

1013

1.2

100

1000

8.5

900

1.1

92

2000

2.0

800

1.0

83

3000

-4.5

700

0.91

76

4000

-11.0

620

0.82

68

5000

-17.5

540

0.74

62

Based on Williams (200S); taken from Aber et al. (200S).

Based on Williams (200S); taken from Aber et al. (200S).

FIGURE 9-4 Cumulus clouds building over the High Tatra Mountains, while the adjacent foreland remains cloud free in this mid-day, summer view near Strane pod Tatrami, Slovakia. Similar conditions prevail in many mountain systems during the summer monsoon season. Taken from Aber et al. (2008, fig. 3).

FIGURE 9-4 Cumulus clouds building over the High Tatra Mountains, while the adjacent foreland remains cloud free in this mid-day, summer view near Strane pod Tatrami, Slovakia. Similar conditions prevail in many mountain systems during the summer monsoon season. Taken from Aber et al. (2008, fig. 3).

higher temperature comfortable for field work and full battery power, say 20 °C, air density is considerably less.

These conditions impact all types of winged platforms, both manned and unmanned. In the case of kites, for example, several components could be adjusted to compensate for decreased air density at high altitude—use a kite with greater intrinsic lift, increase the size of kite, use a train of multiple kites, and reduce the weight of the camera rig (Aber et al., 2008). In general, rigid kites, particularly the rokkaku type, provide the greatest intrinsic lifting power compared with other types of kites (see Chapter 8.4.1). For model aircraft, it has to be considered that lower air density leads to higher flight speed at the same energy input. At the same speed, accordingly, the available weight-bearing capacity would be lower.

Atmospheric conditions also impact lighter-than-air platforms, such as balloons and blimps. Because of the

FIGURE 9-5 Meteorological observatory atop Kojsovska hol'a at 1246 m altitude in southeastern Slovakia. Kite flyers (*) are positioned on the downwind side of the observatory buildings and towers to avoid any chance of mishap. Access to this site required permission and carrying equipment approximately 1 km up a steep path. Photo by JSA and SWA, August 2007.

FIGURE 9-5 Meteorological observatory atop Kojsovska hol'a at 1246 m altitude in southeastern Slovakia. Kite flyers (*) are positioned on the downwind side of the observatory buildings and towers to avoid any chance of mishap. Access to this site required permission and carrying equipment approximately 1 km up a steep path. Photo by JSA and SWA, August 2007.

lower air pressure, hot-air systems at high altitudes have lower lifting power at a given air temperature than they would have in lower regions. On the other hand, the lifting power increases with a larger temperature gradient between the air outside and the air within the balloon. As high mountain areas are usually colder than lower regions, this effect compensates to a large extent for the change in lifting

FIGURE 9-6 Panoramic view of Elephant Rocks in the right foreground and fog-covered San Juan Mountains in the background on the western edge of San Luis Valley, Colorado, United States. Elephant Rocks are erosional features on the edge of the San Juan igneous province. Kite aerial photograph at ~2440 m (8000 feet) elevation. Taken from Aber et al. (2008, fig. 7).

FIGURE 9-6 Panoramic view of Elephant Rocks in the right foreground and fog-covered San Juan Mountains in the background on the western edge of San Luis Valley, Colorado, United States. Elephant Rocks are erosional features on the edge of the San Juan igneous province. Kite aerial photograph at ~2440 m (8000 feet) elevation. Taken from Aber et al. (2008, fig. 7).

FIGURE 9-7 Mount Maestas (left) and Spanish Peaks (right background) as seen from La Veta Pass in south-central Colorado. U.S. highway 160 crosses the bottom of scene. Access to the ground launch site at ~9400 feet (2865 m) elevation was via a jeep trail. Kite aerial photography was conducted with extremely turbulent wind as thunderstorms grew rapidly nearby. Photo by SWA and JSA, August 2008.

FIGURE 9-7 Mount Maestas (left) and Spanish Peaks (right background) as seen from La Veta Pass in south-central Colorado. U.S. highway 160 crosses the bottom of scene. Access to the ground launch site at ~9400 feet (2865 m) elevation was via a jeep trail. Kite aerial photography was conducted with extremely turbulent wind as thunderstorms grew rapidly nearby. Photo by SWA and JSA, August 2008.

capacity. A hot-air balloon operated at 850 hPa pressure and 15 °C air temperature can carry the same payload as it could at 1000 hPa and 25 °C.

High-altitude SFAP often takes place in mountains. Mountain ranges typically create strong local climatic effects, which include colder temperature, enhanced cloud cover (Fig. 9-4), and more precipitation than for adjacent lowlands. Mountain peaks and valleys are well known for rapid weather changes. Swirling wind funnels along valleys and over passes with frequent and abrupt changes in direction and strength; alternating updrafts and down-drafts are routine. Finding a suitable open space for unmanned SFAP can be a challenge in forested mountains, and access to alpine areas above timberline may be quite limited. Areas with good access are often sites with other human structures and activities that could prove risky for tethered platforms (Fig. 9-5). The combination of cloud cover, variable wind, and limited access makes for difficult SFAP in many mountain settings, and small manned aircraft may be particularly dangerous to operate under these conditions.

The authors have conducted considerable high-altitude SFAP with both kites and hot-air blimps, in spite of such limitations. In general, thinner air with increasing elevation is not a serious problem up to w2500 m. Thin air does become more significant above 2500 m, particularly at usual temperatures (20-30 °C) for typical field work during the growing season. High plains, mountain forelands, and broad intermontane valleys offer excellent SFAP situations with relatively open terrain, stable wind, and abundant sunshine (Fig. 9-6). Mountains are more difficult, however, because of frequent cloud cover, gusty wind, and limited ground access (Fig. 9-7).

FIGURE 9-8 Regular pattern of ground control points (arrows) on a 24 m x 36 m, slightly sloping site for vegetation and erosion monitoring near Maria de Huerva, central Ebro Basin, Spain. Red target signals (larger in corners and center) are placed around permanent markers made from metal pipes to allow easy identification in the image. Hot-air blimp aerial photograph by IM and JBR, April 1996.

FIGURE 9-8 Regular pattern of ground control points (arrows) on a 24 m x 36 m, slightly sloping site for vegetation and erosion monitoring near Maria de Huerva, central Ebro Basin, Spain. Red target signals (larger in corners and center) are placed around permanent markers made from metal pipes to allow easy identification in the image. Hot-air blimp aerial photograph by IM and JBR, April 1996.

100 Photography Tips

100 Photography Tips

To begin with your career in photography at the right path, you need to gather more information about it first. Gathering information would provide you guidance on the right steps that you need to take. Researching can be done through the internet, talking to professional photographers, as well as reading some books about the subject. Get all the tips from the pros within this photography ebook.

Get My Free Ebook


Post a comment