Page 52 - Military Technology 12/2018

50 · MT 12/2018 C4I Forum

Modern space-based SAR is intended to serve both military
and civilian users and is able to offer higher-resolution
images than have previously been available.
(All photos via author)

Paolo Quaranta

Space-based Synthetic Aperture Radar

for Remote Sensing

Considerations on remote sensing for military operations. for military commanders and intelligence analysts. The development of
SBR is a real technological challenge due to constraints in weight, size
and power imposed by satellite dimensions, and the extreme radiation,
Radar can operate at night, can see through clouds and other obscu- vibration and thermal operational conditions created during launch and
rants, is not dependent on energy emitted by the target, can identify and in the space environment. Of course, SAR represents a key technology in
track moving targets and can create photographic quality images: for these SBR for remote sensing.
reasons Space-Based Radar (SBR) is fundamental to remote sensing, and
is able to gather information of a type and under conditions denied to other Technologies and capabilities
reconnaissance satellites. Modern SBR systems are based on advanced
technologies such as Ground Moving Target Indication (GMTI), Synthetic New emerging operational doctrine employs high-resolution multi-
Aperture Radar (SAR) and Digital Terrain and Elevation Data (DTED), able channel imaging radars and multiple radar/SAR sensors distributed over
to provide an advanced Intelligence, Surveillance and Reconnaissance the area of interest in a network-centric environment to enhance the
(ISR) system. information quality gained by a single sensor. They offer multiple bene-
In military operations SAR systems for space-based surveillance, recon- fits, such as improvement of the potential for target characterisation by
naissance and target acquisition (RSTA) are essential for a wide variety of exploiting multiple observation angles or using already available signals.
missions. Their ability to function by day and night, their virtual immunity SAR systems are characterised by the possibility of obtaining high angu-
to weather, their capability to localize targets in long- and short-range op- lar resolution from signal spectrum analysis in reception using an active,
erations, their ability to generate highly accurate interferometric 3D maps, coherent radar employing microwaves. The image of the detected region
detection and tracking of mobile targets and classification of objects make is obtained by distributing the value of the electromagnetic wave reflec-
them the perfect sensor for many situations. Military planners identify the ted from the surface (in both module and phase modes) on the areas of
following key capabilities for remote sensing systems: interest. In this system, the detected data undergoes a complex post-pro-
• Day/night and all-weather capability; cessing process known as focusing, based on the Fourier series mathe-
• Long range capability; matical model, which allows the generation of high-resolution spatial im-
• Rapid and large area search capabilities; ages. In particular, taking advantage of this virtual-dimensioned antenna,
• Detection of camouflaged/concealed targets; it is possible to achieve high definition satellite imagery in the order of
• Multi-functional sensing; 1m resolution. In space-based SAR the principle of operation is similar to
• Multi-function detection/ID capability; that in the airborne environment, with the additional advantage, of course,
• Information processing and advanced technologies (with the use of of the increased coverage and worldwide access offered by the satellite
artificial intelligence) for reduced operator workload and training bur- platform, but with the addition of other two systems that are specific for
den; and space-based operations. The first is the radar altimeter, a nadir-looking ra-
• Detection of low signature targets. dar system with a remarkable range capacity which measures surface to-
pography and, in addition, by virtue of the analysis of echo amplitude and
Advanced technologies can be applied to enhance image resolu- shape, can provide some meteorological data. Some radar altimeters use
tion in specific conditions while rapid, wide area search capability and SAR and interferometric techniques to achieve their results. The second
detection of low signature targets are fundamental to modern mission application-specific system is a wind scatterometer, which observes the
scenarios, including maritime applications such as improving detection same portion of earth surface from a number of different viewing angles.
of small, fast attack craft in littoral zones and other areas of strong sea The operational effectiveness of a space-based SAR system depends
clutter. Combining GMTI, SAR and DTED technologies, SBRs are able both on the location of the orbiting satellite and on the system’s level of
to identify and track both stationary and moving targets in near real time technological capabilities. In addition to orbiting altitude, the inclination of
almost anywhere on Earth, at any time and in almost any conditions. In the satellite’s orbit (i.e. the angle between the plane of the orbit and that of
fact, thanks to these technologies, modern SBR provides a global on-de- the equator), must be taken into consideration, because orbital inclination
mand continuous reconnaissance/surveillance facility for both tactical and can influence the area that the satellite observes. With an appropriate incli-
strategic use, furnishing the capability to detect, geo-locate, identify and nation, the satellite can spend more time over particular areas of interest.
track any kind of target under any conditions. These systems provide a For military satellites, an inclination of 20-60° is usually chosen, since this
global collection of ISR data, which has now become an essential facility enables the optimisation of viewing time in all the most interesting latitudes,