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Monday, November 24, 2014
Jaw dropping details of capabilities of Synthetic Aperture Radar on Ofek-10 satellite launched early April 2014

Seeing Everything, from any Place, at any Time
The SAR payload of the Ofek-10 is the second generation of Radar systems of
this type, providing intelligence agencies with the ability to monitor and
track targets effectively
Ami Rojkes Dombe 24/11/2014
http://www.israeldefense.com/?CategoryID=483&ArticleID=3229

Seeing Everything, from any Place, at any Time The Ofek-10 satellite,
launched into orbit in early April of this year, is the second generation
(TecSAR-2) of Radar payload satellites manufactured by IAI. On average, each
development cycle of a Radar payload that offers better capabilities takes
between 3 to 5 years. “The primary change between the first version and this
version is the size of the satellite’s antenna and its power output,”
explains Dr. Uri Naftali, chief engineer of the TecSAR Radar system at the
ELTA division of IAI. “This antenna is larger than that of the TecSAR-1,
launched in 2008, and the satellite receives a higher gain, so
photoreconnaissance ranges are longer and image resolution is higher.”

Not Only Optical

For a number of years now, Israel has had the ability to obtain optical
images from space through the Eros, Ofek, Ikonos and similar satellites, but
these satellites cannot provide images under poor visibility conditions or
during the night. These limitations significantly reduce the effectiveness
of electro-optical payload satellites, to the point that they become almost
useless in areas permanently covered by clouds. On the other hand, SAR
(Synthetic Aperture Radar) payload satellites can produce images of the area
being covered during the day or night and under any weather and visibility
conditions.

The sensor of SAR payload satellites actively “illuminates” the surface, and
owing to the relatively long wavelength it uses, it can provide images even
where other systems fail to do so. The sensor emits electromagnetic
radiation, so it is particularly sensitive to metallic objects that reflect
such radiation. One of the advantages of SAR payload satellites compared to
optical payload satellites stems from the fact that the payload transmits a
controllable signal, thereby eliminating dependence on natural illumination
sources where the signal provided cannot be controlled, as is the case with
optical payload satellites that rely on sunlight, whose power is random.

SAR systems “compel” the Radar to produce resolution in both range and
azimuth. As far as azimuth is concerned, the resolution may be improved by
transmitting from a very long virtual “antenna”, hence the name Synthetic
Aperture Radar. Hence also the importance of the size of the antenna.
Although this technology is not unique to Israel, IAI managed to develop an
advanced SAR payload satellite weighing about 300 kilograms, while other
countries that develop such satellites launch satellites that weigh tons.

Another feature of the SAR payload is polarimetric photography. The Radar
transmits in both vertical and horizontal polarizations, and the difference
between the reception gain values of the different polarizations provides
information regarding the type of particle. Using polarimetry technology and
advanced signal processing, which provides information regarding the
characteristics of the polarized reflection at the single pixel level, it is
possible to identify, for example, whether the elements detected are
man-made or natural, even under complex terrain conditions. “We have
included in the Ofek-10 polarimetric photography capabilities that enable us
to obtain more information about a target compared to the information
provided by TecSAR-1,” explains Naftali.

The design of a small, fast satellite had also stemmed from the desire of
the Israeli intelligence agencies to use the satellite for monitoring and
tracking targets rather than just for scanning large areas. While other
countries are developing satellites for scientific, commercial and other
purposes, where the objective is to cover large areas, in Israel they prefer
to focus on smaller areas, reach those areas at a higher speed and cover
them with a better image quality. “One of the derivatives of the development
of this Radar was the development of a dish antenna for focused coverage, as
opposed to a more rectangular antenna that offers wider coverage,” explains
Naftali.

Optical Payload or SAR Payload Satellite?

One of the questions that arises in the context of surveillance satellites
is whether SAR payload satellites will be able, sometime in the future, to
demonstrate the same capabilities as those of the optical payload
satellites. “There will always be a difference. The SAR payload is not an
optical payload. Even if you obtain the best possible resolution from the
Radar, it will still be different from the images you obtain from an optical
payload satellite,” explains Naftali. “They will not be interchangeable. A
SAR payload has a photoreconnaissance capability during the night, during
the day and under any weather and visibility conditions. Hence, it is twice
as effective as far as the end user is concerned.

“Another ability we developed here at ELTA involves cutting-edge
capabilities for detecting changes – which optical payload satellites do not
possess. While an optical payload satellite relies on light coming from the
sun, which is random, SAR payload satellites rely on the controlled
transmission of electromagnetic radiation, so their change detection
capability is very accurate. We have reached an accuracy level of
centimeters in the measurement of changes. This cannot be provided by an
optical payload satellite. At the same time, optical payload satellites
provide images whose visual character is more easily comprehensible to
humans. These are two different sensors that complement one another.”

As far as future challenges are concerned, Naftali says that IAI intends to
continue the development of their SAR payload satellite line. Apart from
Israel, only a handful of other countries have been able to demonstrate such
capabilities.

So what can we expect from TecSAR-3? “Other challenges are the continued
reduction of the weight and volume of the satellite and extending its
operational service life in space. TecSAR-1 has been in space for almost 6.5
years. We strive for more. We are currently also investing in the aspect of
polarization in order to obtain better quality images,” says Naftali.

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