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Buying Optical Satellite Imagery - continued page 4
9. Cloud Cover
Typical cloud-cover guarantee with new collections is 15 percent or less within the project AOI. Some satellite operators offer an improved cloud-cover guarantee for a cost uplift or the ability to choose a small cloudfree target area that must have zero cloud cover. This option is well suited for infrastructure sites such as airports, mines, and oil and gas installations.
Typically, if the satellite operator can’t deliver a new collect that meets order specifications during the estimated collection window, the customer can either extend the collection window or cancel the order at no charge. With archived imagery, a reduced-resolution preview graphic can be reviewed ahead of time, although it can be difficult to detect small clouds or haze.
10. Delivery Method
Traditional delivery methods have been FTP, DVD and external hard drive. As FTP capabilities have improved and the cost of external hard drives has come down, DVD is being used less frequently. Before ordering a large area with DVD delivery, it’s worthwhile to consider the time required to upload from DVD to hard drive vs. the extra cost of delivery on external hard drive. Heavy imagery users also will benefit from an upgrade to USB 3.0.
Leveraging Professional Guidance
In such instances, an experienced geodata professional can help users understand the acceptable trade-offs for a proposed project. Working with an independent data company, often called value-added resellers (VARs) or channel partners, can help ensure the optimal imagery solution for your specific project/area instead of limiting the range of options to one satellite operator. VARs typically offer imagery at the same price as the source company.
A specialized data company can source DEMs and ground control as needed and can offer custom processing and flexible delivery options. For example, imagery can be ortho output as 16-bit pan plus MS for users with more advanced remote sensing software and three-band, 8-bit pan-sharpened mosaics with contrast adjustment, in GeoTiff and wavelet compressed formats, for users with daily computer-aided drafting (CAD), geographic information system (GIS) and graphics software applications.
In areas where the selection of archived imagery is limited, a value-added vendor can combine imagery from multiple sensors into the same mosaic. In addition, products can be processed to complement each other. For example, high-resolution imagery with superior native accuracy can be used as control to improve the accuracy of medium-resolution images covering larger areas.
Additional Options Abound
The Japanese satellite ALOS no longer is collecting new imagery, but archived imagery collected during its five-year lifespan is available at moderate cost. The range of imaging satellites is too numerous to list, but includes options such as KOMPSAT, EROS, FORMOSAT, the IRS constellation, Resourcesat and Cartosat, among other sensors. Public-domain Landsat and low-cost ASTER imagery can facilitate projects where commercial imagery may be cost-prohibitive; both Landsat and Astrium’s SPOT Image products offer extensive historical imagery archives.