September 26, 2022

The Leica DMC-4 airborne imaging sensor maximizes acquisition efficiency

The Leica DMC-4 airborne imaging sensor improves the imaging performance by 20% compared to previous systems and has a frame rate of 0.8 seconds.

System specifications

The DMC-4 combines several new features and enhancements but probably the most interesting is the cross-track pixel count of this system. At over 31,000 pixels it is the most resolute, large-format frame sensor in Leica Geosystems’ industry segment. This is a 20% increase in swath coverage over the DMC III when collecting the same ground-sample-distance (GSD). The other key, new performance spec is the high frame rate achievable with the DMC-4 of 0.8 seconds. This means customers can collect higher forward overlap or fly faster, or both. For example, the DMC-4 can collect 5 centimeter GSD imagery at 90% forward overlap, flying at 170 knots ground speed. The DMC-4 provides these new benefits along with the one-stop, end-to-end solutions for flight management, gyro-stabilized mounting and high-performance workflow that is bundled with all of Leica Geosystems’ sensors.

Comparison with the DMC III

Compared to the DMC III, the DMC-4 is 20%-30% more efficient due to its increased cross-track pixel count and improved frame rate. However, the DMC-4 has benefits beyond its increased efficiency largely due to the use of Leica Geosystems’ MFC150 sensor modules. The MFC150 module includes the lens, imaging sensor and FMC (forward-motion-compensation, see below) components and brings the experience gained with millions of MFC150 image frames in Leica Geosystems’ TerrainMapper, CityMapper and ContentMapper sensors. The stability, radiometry and exceptional resolution of the MFC150 form the core of the DMC-4 and, because Leica Geosystems has been using the MFC150 for years now, the DMC-4 comes to the market already mature with field proven technology.

The DMC-4’s modular design makes it easier to maintain in the field and more future-proof as new modules become available down the road. Finally, because the DMC-4 utilizes the same mount, inflight systems and workflow as other Leica Geosystems’ sensors, multisensor customers see more flexibility for sensor swaps and can leverage their workflow training and licensing investments as they grow their business.

Forward-Motion-Compensation

The sensor provides superior image fidelity by leveraging the CMOS-based Leica MFC150 camera module with Leica Geosystems’ unique mechanical forward-motion-compensation (FMC). Forward-Motion-Compensation (FMC) means the system physically compensates for the forward motion of the aircraft during exposure. All camera sensors need some amount of time to collect light and store an optimal image. The time to do this is controlled (mostly) by a shutter that opens and closes to expose the digital sensor. The amount of time the shutter is open is variable depending on available sunlight and how reflective the ground features are, but generally between 1/100th and 1/1000th of a second. At normal aircraft speeds the sensor will have traveled several pixels between the time the shutter opens and closes, blurring the pixels. Leica Geosystems corrected for this by physically shifting the sensor during exposure to match the aircraft’s forward movement. This means the sensor can be operated at optimal settings not only for shutter speed, but also aperture and gain, resulting in superior image fidelity.

Standard (S) and high (H) focal length configurations

With over 31,500 pixels across swath, the DMC-4 maximizes acquisition efficiency and improves performance by 20% to cover larger areas with fewer flight lines. Standard (S) and high (H) focal length configurations enable maximum airspace flexibility, providing a comprehensive solution for demanding applications and use cases. The DMC-4 was designed with application versatility in mind, supporting photogrammetry, remote sensing, terrain extraction and vector mapping.

The primary difference between the standard (S) and high (H) configurations is the field-of-view.  The standard, or S version, of the DMC-4 has a 58° Field of View FoV which is very close to the FoV of the prior generation DMC III. The H version has a 45° FoV which is very close to the FoV offered on the popular DMC II 250 configuration several years ago. Customers have told Leica Geosystems that certain requirements are better met with a narrow FOV configuration like the H. Probably the most common is a growing trend for tenders to restrict the building lean, or vertical displacement in orthoimagery products. With its narrower FoV, the H version produces less vertical displacement, or lean, at the outer portions of the frame. This means fewer flight lines are required to meet the requirements of these tenders.

The H version may also better fit some customer’s requirements for collecting at higher flight levels in restricted airspace. For example, the H version can collect 7.5-centimetre (or 3-inch) resolution imagery at 3,000 meters or roughly 10,000 feet. 10,000 feet is a common minimum Above Ground Level (AGL) around major cities and airports around the world.

Leica Geosystems does see that the more traditional 58° FoV of the S version aligns well with the most common requirements and strikes a good balance between collection efficiency and lean displacement. Because it collects at lower altitudes for the same ground sample distance (GSD) compared to the H version, the S system may also be more appropriate for customers operating a non pressurized aircraft or preferring to collect without supplemental oxygen.

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