Quality assessment of ENVISAT Atmospheric mission: i mplication for the scientific user community [email protected] Abstract
Quality assessment of ENVISAT Atmospheric mission: implication for the scientific user community
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 SCIAMACHY 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 missions (GOMOS, MIPAS and SCIAMACHY).
The satellite instruments are subject to performance degradation due to the aging of mechanical and electronic components or due to the impact of platform and on-ground anomalies. 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 SCIAMACHY 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.
Besides the daily monitoring the evolution of key parameters is important for assessment of instrument performances and for mission evolution and calibration plan definition. Further details can be found in the SCIAMACHY bi-monthly report available on-line: http://earth.esa.int/pcs/envisat/sciamachy/reports/bimonthly
Mission and Processing Status
SCIAMACHY mission status (curtesy of DLR SOST)
SCIAMACHY is an imaging spectrometer that records solar radiation transmitted, backscattered and reflected from the atmosphere in the UV/visible, using nadir, limb and sun/moon occultation.
The SCIAMACHY mission performs nominally. No particular anomalies have been detected since begin of mission, instrument unavailabilities are mainly due to single event upsets (SEU).
Ratios of SMR spectra derived from calibrated SMR/ESM during Feb 2006 are shown in Fig. 4. The ratios were determined by dividing the spectra at the beginning of the month to a set of days during the month. The strong features in Fig.4 coincide to emission lines partially formed in the solar chromosphere and are known to change with solar variability.
On 08 May 2006 the NEW operational SCIAMACHY L1 processor (IPF 6.01) will be switched on in NRT (PDHS-K, PDHS-E) and OFL (D-PAC) centers.The operationof L2 NRT 5.04 will be suspended on that day.
With the activation of IPF 6.01 a new set of ADF (static and dynamic) will be required; in this frame a new calibration tool (SCICAL) will become operational and it will replace the ADF generation algorithm implemented in IECF. Furthermore the L2 OFL processor version 3.0 provided by DLR is under ESA acceptance test.
Full mission reprocessing will start at the end of 2006 with IPF 6.01 and L2 OFL 3.0, recalibration at DPQC is already completed.
Instrument and Product monitoring
The L0 monitoring consists in the check of important telemetry data, which give information about instrument performances, in particular components temperatures and important parameters to check in the L0 daily monitoring are the the stability of the detector temperatures.
An example of a L0 daily plot is reported on Fig.1 showing the detector current for the different channels.
Fig 4 – Ratio of Sun Mean Reference during Feb 2006.
Leakage current analysis
This analysis consists in plotting the ratios of the leakage constant part FPN of each month with different time distance of one orbit, one day, one week, two weeks, three weeks and a month. The results of February 2006 are reported below. Sudden jumps can be seen in Fig. 5 for channels 1, 2 between 2 and 3 weeks. They are very small but above the noise level.
Fig 1 – Detector temperatures for SCIAMACHY detector channels
The monitoring of L1b products is currently based on dark current parameters for the different detectors, scattered solar stray light, leakage current, polarization measurement device (PMD) parameters, sun reference spectra, the ADF usage and the DMOP execution plan.
An example of a daily plot is reported in Fig. 2 the Leakage current plot mean noise. In this plot the values of leakage current for various detector and for all pixels are shown, the y axis is the # of measurements, the colours indicate the value of current in binary units.
Fig 5 – Ratio of the leakage constant part FPN.
NO2 consistency check
NO2 monthly average on Jan 2006 are shown on Fig. 6. An artifact due to algorithm anomaly can be seen looking at the excessive NO2 values over the Antarctic region.
Fig 2 – Leakage current plot mean noise
For L2 NRT monitoring significant indicators are the time trend of retrieved values (e.g.: VCD of O3, NO2) and the geolocated plots of VCD and errors for O3 and NO2.
L2 OFL, currently includes monitoring on NADIR parameters (as for L2 NRT) and a check on limb O3, NO2 profiles and its errors. With the new processor version the monitoring will be upgraded as well.
An example of a daily NRT plot is reported in Fig. 3 showing the VCD of O3 in a geo-located map. Ozone VCD are plotted as a function of geo-location for one day of measurements. This plot allows to detect any non-nominal behavior of O3 distribution.
Fig 3 – O3 VCD for one day of measurements.
Fig 6 – NO2 consistency check during January 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):