ForestMapper, a high-precision, airborne visible imaging system manufactured by Space Instruments, Inc. (Encinitas, CA), is hard at work sweeping across the South American sky, gathering digital data about the Amazon basin for Brazil’s national forest service, Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renovaveis (IBAMA).
IBAMA employs images collected with ForestMapper to generate regional vegetation indices, study the ecological impact of pollution, track natural disasters such as floods and fires, and even pinpoint active sites of illegal logging operations that practice selective harvesting of high-value hardwood trees such as mahogany. In Brazil, for instance, the radiometric device is helping detect the unique spectral signatures of various forms of florae, as well as find the fresh skid trails of loggers.
ForestMapper incorporates a pair of high-speed MegaPlus 1.6i CCD cameras built by Redlake MASD, Inc. (San Diego, CA) and custom software to capture and record high-resolution, 10-bit images. This system can be applied to virtually any type of sophisticated aerial mapping, regardless of landscape and locale.
Space Instruments has been designing and building imaging and remote-sensing systems for twenty years. The R&D roots of the ForestMapper extend back to the mid-1990s, when Space Instruments engineered a microbolometer-based imaging radiometer known as the Infrared Spectral Imaging Radiometer (ISIR). This multispectral, infrared imager was operated successfully in August 1997 by the NASA Goddard Space Flight Center aboard the Space Shuttle Discovery.
According to James Hoffman, Space Instruments’ Technical Director, ForestMapper is a fully integrated system designed specifically to optimize imaging performance while taking into account several key considerations, including footprint, user interface, data storage, and cost. ForestMapper is significantly smaller and less expensive than film-based alternatives. The system also delivers real-time quantitative digital data instantly, without the additional materials and processing expenses often associated with film.
ForestMapper’s two high-dynamic-range MegaPlus CCD cameras each contain 1.6 million pixels and can be triggered at selectable frame intervals down to 1.6 seconds to provide the desired geographical overlap in the flight direction. A three-axis mount allows precision alignment of the two cameras (to within a single pixel) in roll, pitch, and yaw directions. ForestMapper’s spatial resolution at 1000 feet is approximately 5 inches per pixel.
Spectral filters can be used to obtain multispectral images for remote-sensing operations. For example, IBAMA has opted to closely align the cameras in all three directions and acquire images at 0.65 microns with one camera and 0.85 microns with the second. These two spectral images are then used to produce a Normalized Difference Vegetation Index (NDVI) map of the scene for vegetation monitoring.
WIDENING THE FIELD
In lieu of using spectral filters, the cameras can instead be pointed to the left and right, effectively doubling the swath of the system as it tracks. Employing this technique yields a 76[degrees] field-of-view, as each of the standard Nikon lenses included with ForestMapper provides a 38[degrees] field-of-view.
The two MegaPlus cameras can be calibrated and controlled individually by the operator through the ForestMapper software. Integration times are selectable from 10 seconds down to 1 millisecond to accommodate an entire gamut of scene conditions. During system operation, a real-time image from one of the digital cameras is shown, as defined by the operator, who can also “grab” and simultaneously display a static image from the live stream. Moving the cursor over the still image reveals radiometric pixel values on a 10-bit scale. Real-time playback of images is possible, as is the ability to digitally “flag” especially important images. The operator is also able to “zoom” to a specific region-of-interest within an image. The operator decides when to start and stop recording images from either, or both, of the cameras. The system displays the rate at which memory is being used and indicates remaining data storage space.
ForestMapper uses a rack-mounted server-computer that holds up to six 36-Gb hard drives for data storage. GPS coordinates, altitude, speed, heading, and camera settings are saved with every recorded image. As images are stored, a complete digital index of the mission is created automatically. The images are saved without any lossy compression–all 10 bits of data are preserved. A dynamic range of 1024 shades of gray allows for effective comparison of “very bright” and “very dark” features within the same image. Distinct pixel values make it simple to apply precise pseudocolor keys to the monochrome images.
Space Instruments provides full training on system usage, guiding new customers through ForestMapper’s extensive complement of features, as well as rendering aid in data interpretation. Hoffman notes that, owing to the system’s easy-to-master user interface, becoming an expert operator is a rather brief process. ForestMapper can also be customized in various ways to meet a given application’s particular requirements. In fact, plans are now being developed, says Hoffman, to create a satellite-based version of the system.