Koen van der Zandena, Jorg versluysb, Tanja Van Achterenc, Michael Francoisd, Jan Vermeirena
aXenics nv, Ambachtenlaan 44, BE-3001 Leuven, Belgium
bOIP Sensor Systems nv, Westerring 21, BE-9700 Oudenaarde, Belgium
cVITO nv, Boerentang 200, BE-2400 Mol, Belgium
dESA-ESTEC, Keplerlaan 1 – NL-2200 AG Noordwijk, The Netherlands
In this paper we will discuss the design, the qualification and the early in space results of a long linear array operating in the [0.9 – 1.7 μm] range for the Belgian Proba-V vegetation mission. The instrument contains 4 bands: 3 VIS/NIR bands and 1 SWIR band.
The SWIR FPA is a long linear array, designed to have the same length as the visual detector array and measures app. 68 mm. InGaAs, grown lattice matched on an InP substrate and operated at room temperature, is selected as the baseline detector material. Due to the length of the linear array it was decided to design the overall FPA of several subparts in a mechanical butting approach.
The 25*25 μm detectors are read out with a ROIC with Capacitive Trans-Impedance Amplifier (CTIA) interface stage. The nominal feedback capacitor is 600 fF, resulting in a sensitivity of 270 nV/e- and a full well charge of 7.5 Mio e-. The analog signal path is further equipped with a Correlated Double Sampling (CDS) stage to reduce the noise and a S&H bank to allow both Integrate Then Read (ITR) and Integrate While Read (IWR) operations.
The power dissipation of the array in slow scan mode is below 900 mW for the FPA. The noise of the array in darkness is estimated to be 3500 e-rms, resulting in a dynamic range of 2200:1.
Prior to launch, the FPA was subject to 60Co, proton and heavy ion irradiation; no permanent damage at moderate doses was observed; (soft) latch-up effects were observed mainly under heavy ion radiation.
After launch all FPAs are working fine, without any initial degradation. We observe some pixels with an increased dark current, which are more difficult to calibrate for radiometric purposes. The origin of this change is still under investigation at this moment.
Keywords: Earth Observation, Vegetation, Proba-V, SWIR, InGaAs, Linear array, CTIA, Mechanical butting