Sensors for remote sensing by Xenics

Sensors for remote sensing by Xenics

The main activities of Xenics are the design and manufacture of linear arrays, FPA and cameras for the Short Wavelength range (SWIR), based on InGaAs detectors. Exactly this wavelength band is of high interest in the remote sensing of vegetation properties. The water (vapor) content of the atmosphere causes a strong absorption at 1.45 μm, but above this absorption peak, the reflectance in the [1.5 – 1.7 μm] band is very interesting to determine the liquid water content in the plants and for the identification of tree types and plant conditions. For the more Mediterranean area the SWIR band is also important to detect wild fire affected areas and even for the detection of active
fires.

In most cases, there is a drive to very long linear arrays, which are geometrically matched to very long linear arrays in the visible and NIR wavelengths range. This means that a pitch of app 25 μm is solicited, which is double the size of the VNIR sensor, and a sensor line length in the range of 35 or 70 mm. Taking into account that most InGaAs detectors are manufactured on 3 or 4 inch wafers, the arrays are taking a large part – if not the full wafer diameter. Additionally it is required that – at least – the pixels in the central part are defect free and fulfilling all electro-optical properties. In order to keep the manufacturing and flight cost within acceptable limits, most often butted array solutions, consisting of smaller sub-arrays,
are preferred.

In 2005-2006, Xenics has worked on a long linear array with 1500 pixels on a 25 μm pitch for the Egyptian experimental remote sensing satellite Egyptsat-1. This array was composed of 3 sensors with
512 pixels each, which were optically butted together by means of a stack of 2 beam splitting cubes. This educational satellite, which was jointly built by the Ukrainian and Egyptian scientists and engineers, was launched in 2007 as a secondary payload on board of a Dnepr
launcher from Baikonour. The SWIR IREI instrument was performing well and has taken some nice pictures from the wildland around the Mediterranean and the Arabic peninsula.

Since 2007 Xenics is involved in 2 important developments for ESA. The first development is the delivery of the Visible, NIR and SWIR linear arrays for the MSI instrument on board of ESAs corner stone
mission Earthcare. The main goal of this instrument is to provide information about the horizontal cloud cover, cloud type as well as aerosol optical properties and densities above the ocean. Each linear
array contains a linear array of 512 pixels, surrounded by 2 multiplexers with 512 inputs. After an extensive engineering phase, Xenics is presently evaluating the pre-qualification devices and manufacturing the qualification models.

Each device type will undergo an extensive qualification cycle, including thermal and mechanical shock testing, life time testing as well as radiation testing. Recent measurements prove that the arrays are
fulfilling the electro-optical requirements and are 40% better than the noise requirement. As a by-product Xenics is also delivering the readout circuits for the micro-bolometer detectors on board of
the BBR instrument on board of the same satellite.

In parallel Xenics is working on the development of a very long linear array for the SWIR channel of Proba-V. This image sensor of 2708 pixels is composed of 3 mechanically butted arrays, with 1024 pixels each. The detector lines are spaced by less than 1.5 mm and have app. 90 pixels in the overlap area to guarantee the full coverage of the swath under all flight conditions. 3 such arrays will be integrated in the
Proba-V instrument, 1 behind each of the TMA telescopes. In this project Xenics is also providing the detector proximity electronics to OIP, the instrument prime. The engineering models of the mechanically butted array are presently under test.

The participation in all this programs shows clearly that InGaAs detectors are the prime choice of the remote sensing community for SWIR imaging and especially for vegetation studies. Recent tests, executed by SSTL and ESA, have also proven the reliability of this
material and – most important – room temperature operation for wavelengths up to 1.7 μm.

World's first InGaAs camera photon emission microscope

Xenics enabled Semicaps to realize the world's first InGaAs camera photon emission microscope in 2004. Since then Xenics and sInfraRed have supported us in our endeavors for better sensitivity and resolution in photon and thermal emission microscopy.

Chua Choon Meng, CEO Semicaps