International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004
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NASA-NOAA study (Mondello et al., 2004) which states
"There is a trend toward higher resolutions and accuracies as
many users are presently faced with using data which do not
comply with their requirements, either because these data are
not present or too expensive". This report clearly indicates an
inadequate evolution of the EO market: that there is a larger
demand than what the EO market offers for data with sub-meter
spatial resolution while a clear surplus is observed for data
offering spatial resolution lower than 10 m (mostly satellite
data) The same trend V is reported with respect to both
positional and elevation precision (insufficient data with
precision higher than 1.5 meter and too much data with lower
precision).
Typically the high accuracy, high resolution data can be found
in aerial RS data, while the low accuracy, low resolution data
originate from satellite observations. Since 2000 several high
resolution satellite data are available (e.g. IKONOS) and
reasonably priced but satellite data suffer from a lack of
positional and vertical accuracy. They are also limited in their
timely availability due to their orbital movement.
3. HIGH ALTITUDE LONG ENDURANCE UAV =
3.1 Carrier
A HALE UAV that is capable to act as a “very low-orbit”
satellite by remaining in free airspace above 14 km (46 000
feet) for months should resolve the inherent drawbacks of both
aerial and satellite platforms. Working with a constellation of
HALE UAVs will combine only the advantages of both
systems.
After a history of some 15 years, these UAVs are now
becoming generally available, especially as energy-storage and
solar cells technology have improved significantly during the
last years. UAVs can either be aircraft or balloons (blimps).
Balloons have a far higher payload capacity and a longer
station-keeping ability but will not be commercially available
within the next 5 to 7 years. Aircraft on the other hand are now
already available and their capabilities will only improve in the
close future.
Both NASA, through the Environmental Rescarch Aircraft and
Sensor Technology (ERAST) program, and recently ESA and
the US MoD (Ministry of Defence) have issued studies or
ordered solutions for unmanned acrial vehicle with a prolonged
stay (months or even years) at stratospheric altitudes (between
12 and 25 km) (Erast, 2004; Heliplat, 2000: Küke, 2000).
As an example, in 2003 a 40 MS contract was awarded by the
Missile Defense Agency (USA) to Lockheed Martin to deliver
a prototype of a High Altitude Airship by 2006 (Dell, 2003).
This platform should be able to carry a payload of 1 800 kg at
an altitude of 20 km and to deliver 10 kW electric power for the
payload. The dimensions of the airship arc estimated at 152 m
length, 49 m diameter and a volume of 480 000 m°.
Another example is the Helios-ERAST solar flying wing that
set a world altitude record for non-rocket powered aircraft in
2001 by flying up to 96 863 ft (29 523 m). In the UK, QinetiQ
worked out the Zephyr aircraft (figure 1. Bermyn et al., 2004).
In this concept, the aircraft has been designed to provide
immediate access to free airspace for prolonged time periods
with a limited payload, at least in the first phase. The current
design calls for a wingspan of approximately 15 m, a payload of
2 kg and 1 kW electrical power for the payload. In 2004 several
test flights are planned while a 3 weeks continuous test period is
foreseen in 2005. The roadmap of this aircraft allows for an
upscaling of the wingspan up to 30 m with a 30 kg payload by
2005/6 and larger wingspan and payload in the following years.
Figure 1. Artist impression of the Zephyr, a light weight HALE
UAV
The Zephyr already complies with present UAV flight
regulations and can thus be used immediately. Vito intends
therefore to use this aircraft in the framework of the
PEGASUS-project to deliver high accuracy and high resolution
earth observation data with a high updated rate, and that not
only for Flanders but by extension in the whole of Europe.
3.2 Instruments
Based on the requirements of the market and keeping in mind
the present limitations on the weight and power consumption of
the payload, the following instruments are being designed or are
currently under construction :
- a multispectral camera by 2005,
- an aerial laserscanner by 2006,
- a thermal camera by 2006, and
-amini-SAR by 2007.
It is the intention to provide imagery that is comparable m
quality to present-day digital aerial cameras. The basic
requirements arc summarized in Table 2.
——À
Flying altitude 12-20 km
Ground resolution 20 cm (at 20 km)
Spectral resolution I0 nm
# spectral channels Initially 4, extensible to 10
# pixels per line 12000 — 30000
Image update At least 100 Hz
Planimetric accuracy Better than 15 cm
Data transfer rate « 40 Mbit/s RT
Continuous use on daily basis | 8 h at equinox
Weight <2kg
Table 2. Basic requirements of the multispectral digital camera.
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