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Welcome to GISWeekly! Digital mapping cameras and airborne digital sensors are a mainstay in high resolution and engineering work, yet these systems operate on completely different principles from each other, consequently providing different capabilities necessary in the collection of image data. Read about these technologies this week in the Industry News.
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Image Data Collection - Digital Mapping Cameras and Airborne Digital Sensors
By Susan Smith
Digital mapping cameras and airborne digital sensors are a mainstay in high resolution and engineering work, yet these systems operate on completely different principles from each other, consequently providing different capabilities necessary in the collection of image data.
I spoke with John Craig, remote sensing director for 3001, Inc., a company that acquires, processes and develops value added products like GIS and linework from imagery taken with digital mapping cameras and airborne digital sensors.
The two cameras 3001, Inc. uses are the Leica ADS40 Airborne Digital Sensor and Intergraph Z/I Imaging's Digital Mapping Camera (DMC). “We are able to use both cameras on different types of work,” said Craig. “Generally Z/I Imaging's DMC is especially great for very high resolution, engineering work and photogrammetry. We've been able to get imagery with a resolution and pixel size of up to 1 inch or 1 /2 inch. The Leica ADS40 is not capable of that high level of resolution. However, one of the advantages of the ADS40 is that you get your imagery in really long strips. If you're working on large geographic areas, lower resolution like aerial coverages, there are advantages because you can do the work more efficiently and cheaper.”
According to Craig, the Leica ADS40 is a line scanning instrument whereas the Intergraph DMC is a framing camera, meaning it takes a picture at a time and each picture is a rectangle. “The DMC is more similar to what people are accustomed to thinking of as a camera. In other words, it takes pictures, and each picture has height and width,” Craig explained. “The ADS40 is a scanning instrument and is more similar to a satellite sensor in that as the instrument passes, as the airplane moves, it captures one line of imagery at a time and builds up the image line by line.”
Z/I Imaging's DMC has only black and white full resolution and the color cameras are reduced resolution. “They used the black and white to sharpen or merge the black and white with the color,” Craig noted. “The result is perfectly fine for most mapping purposes. On the other hand, for applications where you need precise color information, the remote sensing type application, you'd probably prefer the ADS40.”
3001, Inc. has also worked with some hyperspectral data, and usually partner with another company to do hyperspectral jobs. “Basically a hyperspectral instrument works more similarly to a Leica ADS40 in that it also captures strips of data,” said Craig.
Z/I Imaging's Digital Mapping Camera (DMC)
The DMC captures imagery with proven ground resolutions as small as 1½ inches per pixel. Throughout each stage of the project life cycle, imagery captured with the DMC maintains its geometric and radiometric quality - from mission planning all the way through photogrammetric production, client/server image management and storage and distribution.
DMC's framing technology and multi-use sensor are especially useful for acquiring geometrically stable imagery and simultaneously collecting multi-spectral data to enable the generation of black and white, natural color and false-color infrared imagery from a single airborne data set. The camera minimizes the number of flights necessary to obtain high accuracy imagery suitable for downstream photogrammetric processes.
On the business side of things, Z/I Imaging is continuing to merge operations with all the other mainstream activities of Intergraph Mapping and GIS. They are adding their vast expertise of imaging, elevations and image management to the GIS product lines. In some cases, the GIS team helps Z/I with their products. “I would say there is more of an integration of the team,” noted Dr. Terry Keating of Z/I Imaging. “We are putting together industry solutions or focus groups to keep the product focus the same as it has always been. The focus has been extended a little bit to be more aware of some of the GIS trends in the industry.”
Over the past year, they have refined the DMC so that it's not only compatible with their photogrammetric software but also with everyone else's in the industry. There is a waiting list for the $1.4 million product. According to Dr. Keating, “We made sure that the sensor could be used with others just as we made sure that other sensors could be used with our products. We've made some improvements to the scanner, primarily to color balancing. This is a technology where we take the film and get it into a electronic form for the processing.”
Z/I Imaging has introduced a new product called the Z/I Mouse, which is a sophisticated 3D measuring device that allows you to look in stereo onscreen, roll the thumbwheel and get elevations to come on the screen and thereby improve data collection processes in a 3D environment. In addition, Intergraph and Optech Inc. have entered into a strategic alliance to sell a bundled solution consisting of Optech's Airborne Laser Terrain Mapper and the DMC at a special bundled price - leveraging advanced airborne data capture technology to offer cost savings and production efficiency.
Leica ADS40 Airborne Digital Sensor
George Southard, director of global sensor sales for Leica, handles everything that is airborne at the company. He described the ADS40 design this way: “The camera design is based on the proven satellite design of a pushbroom type sensor, which means the CCD, or charged coupled device, is a single line of pixels. As you're flying along you're collecting data line by line rather than patch by patch. That is applied to the airborne environment, so the ADS40 is a satellite to be used in aircraft for imaging.” The camera or sensor has full color red, green, and blue and near infrared channel and also the black and white of the panchromatic channels. “We have basically three cameras in one,”
explained Southard. “You are collecting a continuous strip. We refer to it as a 'pixel carpet,' which is a long thin strip of data that is collected as you're flying. The width of that strip is almost identical to the width of standard aerial photographs that we've been doing over the years. so it's a wide strip but continuous. It is a linear CCD, 12,000 pixels wide and 1 long.” The airplane gets to the end of that flight line and makes a turn and comes back the other way on an adjacent strip that overlaps one strip to the next. The result is that you are dealing with very few files. Those files are quite large, very high density image files. “It improves the overall production flow for
the operator after collection to be able to view relatively few data files and to stitch those files together to create coverages for whole states or counties. It's been proven over the last 2 ½ years to 3 years to be an extremely productive system.”
Modern softcopy systems can handle the pixel carpets quite easily. “You couldn't possibly have done that with an analytical plotter,” noted Southard.
The ADS40 was originally designed in a modular way to be able to incorporate various upgrades and technology advancements as time went on. “There are several types of technological advances coming along that are already impacting the ADS40, one of them is having much more robust and denser storage devices, for the storage of the data onboard, which means we have much smaller storage containers to store all the data. When we originally designed the system we anticipated having quite a large rack of storage disks. Now it's a briefcase sized unit that will hold up to a terabyte of data.