期刊名称：ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences
印刷版ISSN：2194-9042
电子版ISSN：2194-9050
出版年度：2007
卷号：XXXVI-1/W51
出版社：Copernicus Publications
摘要：We have advocated the use a High Altitude Long Endurance Unmanned Aerial Vehicle (HALE-UAV) for remote sensing since 2000. The project, called Pegasus, is now becoming a reality. The platform, an extremely light weight stratospheric aircraft called Mercator-1 has been constructed and is awaiting it's maiden flight in the Spring and Summer of 2007. This aircraft is powered by solar energy and high capacity batteries allowing it to fly for weeks and months on end without landing. As such it can be used a local geostationary system, as it is able to remain above a region persistently. The platform is not bound to an orbit and moves at low speed in a region of the atmosphere where wind speeds are known to be limited. In parallel with the platform development, the design and construction of a high resolution camera to be carried on it has started as well. This camera will produce imagery (panchromatic and RGB color) at 30 cm resolution over a 3 km wide swath from Mercator- 1's operating altitude of 18 km. The MEDUSA phase B project, funded by the PRODEX program of the European Space Agency, was completed in the Autumn of 2006. It produced a preliminary design which demonstrated that all constraints (both environmental and technical) could be met. Based on that, the phase C/D parts of the project were proposed and accepted by ESA/PRODEX. As of November 27, 2006, the final design and construction of the MEDUSA camera has started. The project will run until March 2008. The challenges in the design and construction that are to be met are considerable. The total system should weigh no more than 2 kg, consume no more than 50 W, operate at -50 to -70 °C, transmit all data to a ground reception station in real time and operate autonomously. A detailed study of MTF and SNR has shown that a refractive optical system is the best choice, although it will be heavier than a reflective design. The CMOS sensor at the heart of the camera is being custom designed, which has allowed us to define an unconventional aspect ratio (10 000 x 1200 pixels). This sensor combines the advantages of line sensors (wide swath) and frame sensors (does not rely on external position and orientation sensors for image reconstruction). Frame rates of up to 30 frames per second can be achieved. This characteristic is not needed to guarantee forward overlap, but it is used to reduce image degradation during readout. The readout electronics interface to a command and data handling unit, which manages the data acquisition of imagery and GPS and IMU systems, analyses the image data to adjust integration time for the next image and performs image compression so that all data can be down linked in a 20 Mbit/s stream, over S-band. All subsystems are mounted in a carbon fiber tube with an 11 cm diameter and 1 m length. Special attention is given to the thermal aspects: at night there is no power available for the camera, so it cools to the ambient temperature of -50 °C; during day time, the ambient temperature is even lower, but the electronics and solar irradiation may give rise to thermal stresses. The airborne data (image and ancillary data) are received at the ground reception station and then fed into the data processing system. This triggers a cluster of computers to process and archive the data (which may tally up to 1 TB in a single day). In a first step, all data and image metadata required for further processing are collected in HDF5 Level-1B format (product level definitions are adopted from CEOS). When further processing is required, radiometric and atmospheric corrections are applied as well as georeferencing and orthorectification. The processing system is able to produce fully corrected imagery within hours of the data acquisition. However, for applications that require real time data, the chain processing is simplified, resulting in a turn around time of less than half an hour, which is mandatory if this type of remote sensing system is to be used for disaster management as an integral part of a sensor web. This possibility is the subject of a EC Sixth Framework Integrated Project called OSIRIS
关键词：Digital; Camera; Processing; Hyper spectral; High resolution
