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1.INTRODUCTIONThis paper will describe briefly the tests done on IASI during the end of life and their main results. The content will be divided in 2 parts, one dedicated to the instrument behavior (technological tests) and one dedicated to science tests. Some results are still preliminary because of the deeper investigations needed to have complete analysis. 1.1IASI missionThe mission objectives assigned to IASI are to meet the basic requirements of both the operational numerical weather prediction community and the community interested in the climatology. IASI measurements are used by the research community interested in the atmospheric chemistry. IASI provide improved infrared soundings of the temperature and moisture profiles in the troposphere and the lower stratosphere as well as some of the chemical components playing a key role in the tropospheric chemistry and the additional greenhouse effect. The meteorological mission supported by IASI consists in the determination of the atmosphere characteristics (vertical profile of temperature and concentrations of atmospheric constituents) from the high spectral resolution spectra sent to the Earth by IASI in the thermal infrared [645- 2760 cm-1] 2.TECHNOLOGICAL TESTS2.1IASI-EOL-13: IASI REDUNDANCIES2.1.1Objective and progress of the testThe purpose of the test was to check the remaining redundancies of the instrument that have never been exercised in space before; potentially some knowledge could be gained about the ageing effect after a long stay in space in cold configuration (non-powered). The two redundancies tested was the power of the laser 2 (use for metrology) and the DPC5 (calculator for the science data) 2.2IASI-EOL-16: INVESTIGATION ON CSQ ANOMALIES2.2.1Objective and progress of the testDuring the life of IASI-A, a major anomaly occurred and decision has been taken to move to side B. This anomaly was a very high increase of the CSQ flags (Cube corner Speed Quality error) which detects an instability of the cube corner speed during the interferogram acquisition. After moving to side B this anomaly disappeared. The objective of the test was to characterize more finely the CSQ anomaly on nominal and on redundant sides, by testing several values for the low and high CSQ detection thresholds. The objective was to obtain a more precise knowledge of the amplitude and sign of position errors causing the appearance of CSQs and to provide work around solutions for IASI-B or IASI-C in case of similar anomalies. Because of various problems during the test process, exploitable data are only available for side B. 2.2.2Main resultsAfter the test, completion of statistics have been done on the percentage of acquisition for which a CSQ anomaly appeared depending on the threshold. Looking at these data several points can be noticed and investigated:
All these behaviors are compatible with the ones seen on earth before the launch so we can’t say if there is a problem due to ageing on the mechanism, but if there is, this effect is very small after 15 years in orbit. 2.3IASI-EOL-01 / 02: LFD RELEASE and CD stop2.3.1Objective and progress of the testThe Locking Filtering Device (LFD) was implemented on IASI to ensure a decoupling between the platform and the instrument in order to prevent micro-vibrations coming from the METOP platform and impacting the quality of IASI data. However, this option was never exercised and there was no in-orbit experience of IASI in this configuration prior to the test. The objective was to test the deployment of all the 3 LFDs, taking into account that there is no direct way to validate the success of the release of the LFD. After a long stay in space, the release might be partial and very slow because of the aging of the elastomer materials. Then we stop the compensation device in order to give more chance to see the effect of the LFD release. Indeed the Compensation Device (CD) was introduced in the IASI design to compensate the dynamics perturbations generated by the Corner Cube Functional Device (CCFD) in the configuration where the LFD are deployed; in this configuration, the interface between IASI and the satellite PLM is non-rigid. 2.3.2Main resultsThe release of the LFD Shape Memory Alloy (SMA) run as expected. The variation of the SMA temperature showed a plateau, confirming the phase transition and thus the elongation of the material. However we didn’t see any effect on the SCAO side after the LFD release even when the CD has been turn of. There is 2 hypothesis. First one the elastomer material which had been squeezed for many years in space, had lost elasticity and the capacity to expend the mechanism. Second hypothesis: the expansion was too slow to be noticeable within the duration of the test. At the end of the test, a small impact on the noise correlation matrix can be seen. These differences seem to demonstrate that the release of the LFDs tend to slightly decrease the level of micro-vibrations observed on IASI instrument. 3.SCIENCE TESTS3.1IASI-EOL-15: Local improvement of spatial sampling3.1.1Objective and progress of the testThe objective of the test was to reduce the swath by dividing by 8 the spacing between consecutive FOR (from ~48 km to ~6 km) and therefore increase the spatial density of the soundings. For that the behavior of the scan mechanism has been modified in order to increase the spatial density of the sounding. These modifications had’nt modified the quality of the SCAN behavior 3.1.2Main resultsThe scientific results of this test aren’t available until now but some studies to assess the quality of the data have been done to be sure that scientific analysis based on these data are manageable. We first seen that during the test the behavior of the SCAN remain compliant with the requirements: the SCAN has been controlled has expected and the behavior was stable. All quality criteria suggest that the data are of sufficient quality (equivalent to the nominal quality) to be used for scientific analyses: 3.2IASI-EOL-18: NEDT improvement in B1 on 1 sounder pixel3.2.1Objective and progress of the testThe objective of the test was to reduce the temperature of the detectors and check the improvement of radiometric noise in spectral band B1. The decrease of temperature is obtained by switching off 3 of the 4 pixels of the sounder. The idea was to be able to deliver some data closer to the performances expected for IASI-NG 3.3IASI-EOL-03: Inter calibration of Metop-A, B & C3.3.1Objective and progress of the testThe purpose of the test was to use the opportunity given by the deorbiting of Metop-A and the change of the geometric configuration of the METOP constellation to acquire Simultaneous Nadir Observations (SNO) data by IASI-A and IASI-B or by IASI-A and IASI-C over the Earth poles. The duration of this test was short: only 8 days, so there were few Common Nadir Observations between IASI-A and IASI-B or IASI-C. 3.4IASI-EOL-17: IASI limb pointing3.4.1Objective and progress of the testThe backflip maneuver of METOP-A planned at the end of the EOL test campaign, gave the opportunity to acquire measurements of the atmosphere in Earth Limb directions which has a potential scientific interest and can provide a comparison between IASI and other limb atmospheric sounders. The acquisitions of measurements in the Earth Limb direction provided opportunities to test or validate the spectroscopy and radiance modelling in new conditions, especially in non-local thermodynamical equilibrium state. REFERENCESBlumstein D.,
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