Key performance indicators
- 3 x 1024 pixels for wide ground coverage and high resolution imaging
- Correlated Double Sampling (CDS) for improved noise performance
- In‐flight selectable integration time and gain selection to adapt to illumination conditions
- Based on InGaAs technology with excellent SWIR sensitivity up to 1.7 um
- Selectable frame rates up to 10 kHz for maximum flexibility
- Full environmental and radiation qualification for space applications
- 25 x 25 um2 pixel size
Earth observation by a satellite can reveal lots of detailed information on vegetation, clouds, humidity and other atmospheric conditions. A linear array operated in a push broom mode is the ideal tool for this. The Xlin-1.7-3000 detector is specifically designed for this and consists of 3 sub-arrays of 1024 pixels each, mechanically butted to achieve a virtually linear array of >2900 pixels. A small overlap is introduced to allow for perfect stitching of the 3 individual images. The detector is specifically designed for use in space and has successfully completed a full qualification program on environmental, life and radiation tests.
The detector allows for maximum in-flight control by the user, to switch line period, integration time and gain on the fly. In this approach, the user can adapt to the specific conditions and needs to always get the maximum performance out. E.g., modification of settings can vary in function of day/night conditions, ice/desert/vegetation/water inspection, global/detailed imaging etc.
The assembled InGaAs array is 73.2 mm long, consisting of 25 x 25 um2 pixels yielding a Quantum Efficiency of 75%, combined with an MTF of 50% in the range up to 1.7 um. The maximum pixel rate is 12.5 MHz, yielding a minimum line time of 100 us with one output per sub-array. Pixel operability is guaranteed to be better than 99%. Pixel well depth can be varied by the gain setting from 60ke- (high sensitivity) all the way up to 10Me- (high dynamic range). The detector is supplied in a 72-pin metal can package to allow for excellent temperature control and hermetical seam sealing with a metal lid with window.
Figure 1 is the first raw SWIR image transmitted by the Proba-V satellite to the ground station. It shows excellent central on-ground resolution of 100 meters, with a swath of approximately 400 kilometers. Having such high-quality images without calibration correction, underlines the high intrinsic performance of the InGaAs sensor, the ROIC and the corresponding read-out electronics. The stitching of the individual images of three mechanically butted InGaAs arrays results in the typical shape of the image with an upward offset of the central 1024 pixels. Proba-V is equipped with three such detectors, expanding the total swath to 2200 km (divided over approximately 9000 pixels) with a reduced on-ground resolution of the outer sensors. With the support of Xenics, Proba-V is set to provide the world with valuable daily updates of the global vegetation status.
Figure 2 shows a global picture of the arrays, butted on a gold-coated boat and individual ROIC’s. All this is mounted on an alumina substrate, together with some passive components.
Figure 3 gives a bird eye’s view of the overlap region between two arrays, showing the bond wires connecting the individual pixels.