MIPAS

1. Quality assessment of ENVISAT Atmospheric mission: implication for the scientific user community mipas@dpqc.org Abstract The objective of this poster is to highlight the importance of the instrument and products monitoring and to show the implication of this task for the scientific user community. We focus our attention on the MIPAS instrument on-board the ENVISAT ESA platform and we present some example of quality monitoring results which have significant impact on science data quality. Monitoring activities in support to ENVISAT The quality assessment activities of ESA Earth Observation missions (ERS, ENVISAT, GOCE in the future ) are today performed by the DPQC organization, a Serco-Datamat consortium of specialized companies which provides a service to ESA. The DPQC atmospheric team, which involves expertise from Serco, ACRI and DLR, is responsible for the monitoring of the three ENVISAT atmospheric mission (GOMOS, MIPAS and SCIAMACHY). Introduction • The DPQC group is furthermore responsible for many other activities related to the operational mission support. The DPQC tasks for the ENVISAT mission support can be summarized in the following: • Daily and long term monitoring of instrument health • Daily and long term monitoring of products • Anomaly investigation and performance assessment • Calibration activities and delivery of auxiliary data files • Maintenance and support for IPF evolution and implementation • Mission support, reporting and attendance to progress meetings • Answer to general request from users The satellite instruments are subject to performance degradation due to the aging of mechanical and electronics components or to the impact of platform and on-ground anomaly. Besides, the operational processor, which generates the products, is a compromise between extraction of optimal information from the measurement and the constraints of processing and dissemination resources. As a result the quality of the products arriving to the scientific user community can be variable due to several anomalies. The quick detection of instrument or products anomaly is then crucial for instrument safety and for optimization of data quality. In this poster we will address this problem considering the ENVISAT MIPAS instrument. The quality control baseline will be outlined and some examples of significant daily and long term monitoring will be reported; furthermore the implications of this activity for the scientific users will be underlined. MIPAS Performance assessment Besides the daily monitoring the evolution of key parameters is important for assessment of instrument performances and for mission evolution and calibration plan definition. Examples are shown here below. Further details can be found in the MIPAS monthly report available on the web: http://earth.esa.int/pcs/envisat/mipas/reports/monthly/ Mission and Processing Status MIPAS is a high resolution FTS which measures IR atmospheric emission in limb geometry. The original mission was suspended on March 2004 due to increase of interferometer speed anomaly. MIPAS “new” mission scenario • The “new” RR mission started routinely on January 2005 and is still going on. The measurement scenario was drastically changed. In particular for instrument safety the following options were adopted: • Spectral Resolution reduced to 41% of original one • Discontinuous measurement (around 30% duty cycle) • Besides two options were adopted for science purpose: • Over-sampling of the vertical domain: limb spacing is lower than FOV • Floating (latitude dependent) tangent altitude to investigate tropopause Temperature and Cooler monitoring. In Fig. 5 is reported monthly trend of important instrument parameter during Jan 2006. In particular on the upper part the IDU and MIO temperature, in the lower part the cooler displacer and compressor vibration, these latter parameters are closely monitored during the mission, since any cooler anomaly could dramatically affect instrument health. Fig. 5 shows that during Jan 2006 the temperature levels were stable, while the cooler vibrations show strange spikes which exceed the warning level of 8 mg. The cause is probably the inclination of the platform during this part of the year. The situation came back to nominal by the end of the month. • The speed anomaly is still occurring, the investigation is ongoing, so far we learned that: • Turn-around failures are linked to INT temperature • Bearing are degrading • Mission interruption and low duty cycle are favorable for the instrument The NRT mission was suspended on March 2004 in order to update the algorithms to the new measurement scenario. OFL processing of the RR mission has started on Feb 2006 with the current IPF 4.65 and the data are available via ftp on D-PAC server.The Aug-Sept 2004 data were processed up to L2, the other RR data were processed up to L1b. Instrument and Products monitoring • At a first stage the products monitoring consists in the daily check of the products availability and format in relation to mission planning. • The QUADAS daily monitoring/reporting tool nowadays is implemented for the following MIPAS products: • L0 NRT (checking instrument health) • L1 and L2 OFL (checking data processing quality) • L0 daily NRT report are available on the web: http://earth.esa.int/pcs/envisat/mipas/reports/daily/Level_0_NRT/ Fig. 5 – IDU, MIO temperature and Displacer, Compressor vibration for Jan 2006. • Gain long term trend • The gain accumulation rate is reported in Fig. 6. The points are the maxima of relative variation of gain in band A, the calculation is weekly updated. This plot shows the evident effect of ice contamination during Jan-May 2005 resolved with the decontamination of June 2005. • A gain recalibration was needed in order to ensure good data quality. • NESR is increasing due to this ice contamination • It is also evident the passive decontamination effect of last ENVISAT anomaly of 6 Apr 2006. Level 0 The L0 monitoring consists in the check of important telemetry data which give information about instrument temperatures (IDU, MIO, INT, CBB), slide performances and cooler vibrations. Each time a significant parameter exceed the warning level an alert is sent to FOS and the anomaly is investigated with the support of industry (Astrium). Two example of non-nominal behavior are given below for two critical instrument parameter: CBB temparature and cooler vibrations. In Fig. 1 the Cooler vibration recorded during 6 Jan 2006 shows strange spikes due to variations of platform illumination condition. In Fig. 2 the daily plot of CBB temperature shows excessive value after the ENVISAT PLSOL anomaly of 6 April 2006. Fig. 1 – Cooler vibration during 6 Jan 2006 Fig. 6 – Gain long term accumulation rate from Jan 2005 up to Apr 2006. Fig. 2 – CBB temperature after the recovery due to PLSOL anomaly. Level 1 Concerning L1 monitoring significant indicators are the PCD quality flag, the number of spikes and corrupted sweeps, the number of FCE, the NESR level and the ADF usage. In particular a wrong ADF usage, especially for the gain calibration could lead to bad quality of the spectra and systematic error in the products retrieval, see example below. LOS long term trend In Fig. 7 is reported the MIPAS mispointing since start of mission updated to the end of April 2006. The relative error is the one to be considered, since it takes into account the commanded bias. In this plot it is evident the correction of the seasonal trend after the upgrade of the on-board s/w on Dec 2003. The trend in the last months seems stable with a relative bias of few mdeg. L1 ADF usage anomaly. The D-PAC center didn’t receive correct ADF (due to PDS problem) and the L1 products were generated with outdated ADF from 8 to 22 Feb 2006. As a result the critical gain calibration of the spectra was strongly affected by this anomaly. See in Fig. 3 the plots of NESR level during 21 Feb 2006, where the red level shows excessive noise. In the band A.  The scientific community was alerted not to use these products, the products were deleted and reprocessed with correct ADF. Fig. 7 – MIPAS pointing error since start of mission. Level 2 • Quality check of scientific data • During Feb 2006 the interferometer suffers from increased anomaly rate, a quality assessment on the scientific data was carried out in order to see if the slide anomaly affects the quality of the L1b spectra. • No evidence of quality degradation was found; indeed the PCD flags of the MIPAS 4 bands is plotted in Fig. 8 showing good data quality (the green means no corrutpion). • The anomaly highlighted in Fig. 8 (see black points) at the same geo-location is due to IPF implementation error: IPF write wrong DSR in the L2 products. Fig. 3 – NESR plot during 21 Feb 2006: each square corresponds to a scan. The monitoring of L2 data is particularly complex and many indicators are taken into account; the most important parameters are the time trend plot of retrieved parameters, the LOS pointing Vs retrieved altitudes, the MW offset and the chisquare values. The detection of one L2 anomaly need a long investigation since many source of error can be responsible for non-nominal behaviour (IPF, ADF, L1, L0, ...). An example of L2 anomaly is given below. L2 non-nominal number of succesfull retrieval. The L2 plot of Fig. 4 shows the retrieval summary results for one day of RR measurement (21 Aug 2004). A problem in the retrieval of p-T for some orbit (note that in the plot 7 should be the nominal value corresponding to nominal # of retrieved ESA products). After the investigation it was found that the problem is due to corruption in L1 spectra, in the band D, while the other bands are good. A processor change will be suggested in order not to flag as corrupted one sweep if only one band is corrupted. Fig. 4 – Number of successful retrieval for the 21° Aug 2004 RR data. Fig. 8 – PCD quality flag in MIPAS band A, AB, B and C during Feb 2006.. Source of information The monthly reports for each instrument are publicly available on the web at the pcs web page (see screen shot on the right): MIPAS http://earth.esa.int/pcs/envisat/mipas/reports/monthly/ GOMOS http://earth.esa.int/pcs/envisat/gomos/reports/monthly/ SCIAMACHY http://earth.esa.int/pcs/envisat/sciamachy/reports/bimonthly/ Instrument unavailability http://envisat.esa.int/instruments/availability/ Products disclaimer http://envisat.esa.int/dataproducts/availability/disclaimers General request eohelp@esa.int