ARTEMIS has been designing, building, tuning and testing RF assemblies for nearly 15 years. Each of our products is built in-house to stand up to the rigorous environmental and structural challenges of airborne operation. We have also built spaceborne sensors and communication systems, and we are familiar with the quality and attention to detail required when a system needs to "just work."
Our facility in Hauppauge, NY contains everything necessary to build housings, circuit components, and unit assemblies as well as test them in a variety of atmospheric and physical stress conditions. We pride ourselves on producing hardware that will endure and operate in the often unpredictable environments they are placed in.
Synthetic aperture radar (SAR) is a unique technology which is able to create high-resolution images of the ground beneath an aircraft. Although not meant to replace optical imaging systems, SAR has numerous features which make it an invaluable companion to traditional cameras. For instance, radars can create images through clouds, fog, smoke or dust regardless of the visible lighting conditions. SAR systems also have the same resolution regardless of altitude so flying higher doesn't mean that fine details are lost.
ARTEMIS SAR systems use the latest digital processing techniques to produce high-fidelity stripmap images in real-time or near-real-time. Our systems are extremely versatile and have been successfully configured for a wide variety of airborne platform, altitude, swath-width and resolution requirements.
Traditional SAR processing algorithms only support straight-line stripmap imaging modes. ARTEMIS uses a GPU-accelerated, time-domain backprojection algorithm to reconstruct well-focused images from curved or circular flight lines. This means that the SAR can circle an area of interest and collect data continuously. The data is then processed into multiple "slices" which can be played like a movie, or they can be combined into a single image with a "max-hold" effect.
The ability to process circular paths means that ARTEMIS SAR systems can be used to track changes in a particular area. It also presents targets from many different aspect angles which can aid in identifying different types of objects.
The high resolution SAR mode trades a wide coverage area for extremely high resolution imagery of a particular spot. Depending on the system configuration and the needs of the end user, a gimbal may be configured to keep the antenna pointed at a single spot as the aircraft passes by. This spotlight mode can improve along-track resolution and the aspect angle diversity of the resulting image. Using a high-resolution mode can be likened to "zooming in" with an optical sensor.
ARTEMIS radars can be configured during flight through a standard Ethernet interface. The systems' inherent flexibility offers a wide range of resolution, swath, and altitude settings. If an area of interest is discovered in a wide-area-coverage mode, the radar can instantly be switched to a high-resolution or spotlight mode and the area re-imaged before the aircraft leaves the vicinity.
Radar systems are built to operate in a specific frequency band. Different frequencies will often reveal different features in the exact same scene. This is roughly analogous to the difference between infra-red, visible, and ultra-violet optical cameras. In SAR imaging, high frequencies such as X- and Ku-Band will form an image that is similar to the optical images we are used to. Low frequencies such as UHF and L-Band will often pass right through small or thin items to produce a different view.
While most radar systems can operate in only one frequency band, the ARTEMIS SlimSAR is built to be frequency-agile. The core system operates at L-Band, and add-on block converters enable other frequencies. The SlimSAR currently operates at UHF, L-Band and X-Band and can simultaneously collect images in any two of these bands. This unique and powerful capability sets the SlimSAR apart in its field.
A pair of polarized sunglasses will filter out light waves which are not oriented the same as the filtered lenses. SAR systems can operate in a similar fashion by transmitting and receiving only linearly-polarized electromagnetic waves. In general, the most useful linear polarizations are horizontal (H) and vertical (V) with respect to the imaged scene. The abbreviations H and V are often put together to represent the polarization which was transmitted, and that which was received, e.g. HH or VH. Polarimetric SAR images contain additional information about the types of objects in an imaged scene.
The ARTEMIS SlimSAR is capable of fully-polarimetric operation. This means that four separate SAR images can be formed from HH, VV, HV, and VH polarizations in a single pass.
The concept of change detection is a simple one: you create an image of an area you want to study, make another image of the same area at a later time, and then compare the two. Since SAR provides its own illumination source and the reconstructed images (in ARTEMIS' case) are always geo-located and projected to a DEM, there are no differences in lighting/shadows or aspect angles between the images. Additionally, SAR is a coherent imaging system which means that differences to within a fraction of a wavelength (a few centimeters at X-Band) can be detected. Using statistical methods to combine information from different polarizations during change detection also increases the probability of detection for difficult-to-see targets.
ARTEMIS SAR systems can operate in multiple frequency bands and polarizations during a single flight and are uniquely configured to be able to take advantage of both coherent and polarimetric change detection techniques.
Sometimes it is obvious how different polarizations can provide more information in a SAR image. For instance, a predominantly horizontal feature (such as power lines) will appear much more brightly in a horizontally polarized image. There is, however, a wealth of additional information about a scene which can be extracted from fully polarimetric data sets. Statistical decompositions of polarimetric SAR data can yield information about the class of radar scatterers in a scene.
ARTEMIS has developed software which decomposes polarimetric data from the SlimSAR into classification maps which distinguish between areas of vegetation, cleared ground, roads, and various man-made targets. This type of software adds significant value for the radar end user.
In general, the most time- and labor-intensive part of utilizing any sensor is not installing and operating it, but rather analyzing resulting data to find useful information. SAR systems are often used to search for a certain class of target or feature which the system is uniquely situated to find. A human analyst could spend many fatiguing hours scanning through numerous SAR images just to find something that he or she may be interested in.
Machine learning algorithms reduce the strain on human analysts by automatically nominating areas which are similar to targets or features which the system has been "trained" to look for. ARTEMIS has developed machine learning routines which combine information from multiple frequencies or polarizations in order to give the computer as much information as possible when distinguishing between different types of targets.
SAR interferometry is an advanced technique which uses multiple images collected from slightly different angles to extract height information about the imaged scene. Highly accurate interferometric height maps can be created in a single pass using a radar which supports two simultaneous receive channels if the two receive antennas are mounted with a known offset. It is also possible to fly over the same area twice with slightly offset flight paths and carefully align the two resulting images for interferometry. This is known as repeat-pass interferometry.
The ARTEMIS SlimSAR and MicroASAR are both capable of simultaneous, multi-channel collections which makes them a natural fit for interferometric applications. ARTEMIS radars have been successfully used in both single-pass and repeat-pass interferometry modes for a number of scientific and tactical applications.
Polarimetric interferometry is a special case of SAR interferometry which requires two fully-polarimetric collections from slightly offset antennas. A fully polarimetric dataset contains information about the type of radar scattering caused by trees, vegetation, bare earth, and other scatterers. When this information is combined with the height that can be extracted from SAR interferometry, it is possible to construct an elevation model for not just the ground, but also the heights of trees and vegetation in an area. The SAR is capable of imaging a significant area making this technique very useful for obtaining detailed information about a forested area.
Using the SlimSAR's multi-channel fully polarimetric collection mode and our repeat-pass interferometry processing algorithms, we have successfully demonstrated tree height estimation through polarimetric interferometry.
In its simplest configuration, a SAR system creates a static image of a scene that is assumed to be unchanging while the aircraft flies overhead. In reality, many of the objects in the scene may be moving. Moving targets are generally smeared and displaced in a SAR image, making it difficult to tell what the object was and what direction it was going.
ARTEMIS has the capability of detecting these moving targets and then using advanced processing techniques on collected SAR data to reconstruct the movers original location, speed, and direction of travel.
SAR is a powerful tool which provides a wealth of information about a given area being imaged. The true potential of any sensor system is only achieved, however, when the end user can get the information he or she wants and compare it with output from other sensors and systems. ARTEMIS processing algorithms work seamlessly with standard transmission formats such as NITF 2.1, SICD, GeoTIFF and KML allowing the final data products to be easily integrated into most existing exploitation and analysis tools. Additionally, ARTEMIS has the experience and expertise to integrate our SAR products into any custom processing and exploitation workflow.