egu 2009 vienna 19 – 24 apr 2009 ice on ir sensors: mipas case ice contamination on satellite ir...
TRANSCRIPT
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Ice contamination on satellite IR Ice contamination on satellite IR sensors: the MIPAS casesensors: the MIPAS case
F. NiroF. Niro(1)(1), T. Fehr, T. Fehr(2)(2), A. Kleinert, A. Kleinert(3)(3), H. Laur, H. Laur(2)(2), P. Lecomte, P. Lecomte(2)(2) and G. Perronand G. Perron(4)(4)
(1) Serco S.p.A., Via Sciadonna, 24, 00044 Frascati, Italy(2) European Space Agency (ESA) - ESRIN, Via Galileo Galilei, 00044 Frascati, Italy
(3) Forschungszentrum Karlsruhe GmbH, Institut für Meteorologie und Klimaforschung (IMK), P.O. Box 3640, 76021 Karlsruhe, Germany
(4) ABB Bomem Inc., 585 Blvd. Charest East, Québec, G1K 9H4, Canada
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Intro
Calibration
Ice effects
Summary
What’s next
slide 2
ContentsContents
IntroIntro
Intro
MIPAS on ENVISAT: instrument overview and status
Calibration
MIPAS Calibration strategy and requirements
Focus on the radiometric calibration: the gain function
Ice effects
The ice effects on MIPAS
Ice on AATSR and SCIAMACHY
Summary
Summary and lessons learned
What’s next
The ENVISAT and MIPAS mission extension beyond 2010
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Intro
Calibration
Ice effects
Summary
What’s next
slide 3
MIPAS on ENVISAT MIPAS on ENVISAT MIPAS is a FTS measuring the limb atmospheric emission in the mid-IR
spectral range, 4.15 µm – 14.5 µm, 685 – 2410 cm-1 The INT is a dual slide. The two output ports are directed to two sets of
four duplicated detectors. This allows for redundancy and for enhanced radiometric performances
The detectors and their fore optics are stored in the FPS and cooled down to 70K with a pair of Stirling-cycle coolers
IntroIntro
Spectral range: 685 - 2410 cm-1
(5 bands)
1020-1170
AB1215-1500
B1570-1750
C1820-2410
D685-970
Acm-1
Spectral range: 685 - 2410 cm-1
(5 bands)Spectral range: 685 - 2410 cm-1
(5 bands)
1020-1170
AB1020-1170
AB1215-1500
B1215-1500
B1570-1750
C1570-1750
C1820-2410
D1820-2410
D685-970
Acm-1685-970
Acm-1
Fourier Transform IR (FTIR) Limb Sounding Spectrometer
day and night measurements
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Intro
Calibration
Ice effects
Summary
What’s next
slide 4
““Optimized Resolution” missionOptimized Resolution” mission On March 2004 after an increase of INT velocity errors (speed of one or
both slides exceeds 20% of the nominal speed) the MIPAS mission was suspended and several tests made to find the best configuration
The new scenario started on Jan 2005 with: Spectral resolution was reduced to 41% of the original one (0.0625 cm-
1 instead of 0.025 cm-1) Vertical and horizontal sampling of the atmosphere was increased
owing to the shorter measurement time Duty cycle reduced to about 40% in order to reduce INT errors
IntroIntro
Increase of vertical samplingIncrease of horizontal sampling from FR (red) to OR (blue)
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Intro
Calibration
Ice effects
Summary
What’s next
slide 5
MIPAS instrument statusMIPAS instrument status High number of INT velocity errors were still observed during 2005 – 2006 The errors type was analyzed in details it was found that it depends on
Temp (beam-splitter), friction (bearings) and # of initialization (start-up) Corrective actions were undertaken that allow to decrease the number of
errors and increase duty cycle up to 100% since Dec 2007
Mipas instrument availability since launch
0%
20%
40%
60%
80%
100%
Nov-02
Mar-03
Jul-03
Nov-03
Mar-04
Jul-04
Nov-04
Mar-05
Jul-05
Nov-05
Mar-06
Jul-06
Nov-06
Mar-07
Jul-07
Nov-07
Mar-08
Jul-08
Nov-08
IntroIntro
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Intro
Calibration
Ice effects
Summary
What’s next
slide 6
MIPAS products and calibrationMIPAS products and calibration The MIPAS operational products are:
Level 1: Calibrated atmospheric emission spectra Level 2: atmospheric profiles of p-T and main target species (O3, H2O,
CH4, N2O, HNO3, NO2) The L1 calibration process consists of:
Radiometric calibration: The process of assigning absolute values in radiance units (W/(cm2 sr cm−1)) to the intensity axis (y-axis)
Spectral calibration: The process of assigning absolute values in cm−1 to the wavenumber axis (x-axis)
LOS calibration: The process of assigning an absolute LOS pointing value to a given atmospheric spectrum
CalibrationCalibration
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Intro
Calibration
Ice effects
Summary
What’s next
slide 7
MIPAS L1 radiometric MIPAS L1 radiometric calibrationcalibration
The radiometric calibration is a crucial step of the L1 processing since an error in this calibration directly translates into an error in the retrieved profiles. The radiometric calibration requires: Deep space (DS) measurements to correct the scene for self-
emission of the instrument. DS measurements are done frequently to account for variation of the instrument Temp along the orbit
Blackbody (BB) measurements followed by an equivalent number of DS measurements to calculate the radiometric gain function.
The gain function is calculated once per week, this allows to fulfill the requirement of gain accuracy (1%)
The radiometric gain G is calculated from the measured BB and DS radiances (SBB and SDS), and the theoretical BB radiance (LBB):
The measured radiance (LX) is calibrated using this gain function, the observed radiance of the scene (SX) and of the offset (Sc) closest in time
DSBB
BB
SS
LG
CalibrationCalibration
)( CXX SSGL
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Intro
Calibration
Ice effects
Summary
What’s next
slide 8
Weekly changes of gainWeekly changes of gain Changes in the gain function are caused mainly by changes in instrument
transmission, due to ice. The ice is somewhere in the optical path in the focal plane subsystem which is cooled to 70K
The ice is either on the edges of the entrance hole (of the focal plane subsystem) and/or on the dichroics (splitting the light to detectors) and/or the detector windows
Often the MLI (multi-layer insulator) may trap water from the air on-ground. This trapped water evaporate (outgassing) with increase of temperature and can deposit in coldest part of the instrument with formation of ice layer
Ice effectsIce effects
Ice absorbanceGain changes
Gerakines et al., Astronomy and Astrophysics 296, 810, (1995)
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Intro
Calibration
Ice effects
Summary
What’s next
slide 9
Gain variation in band AGain variation in band A Ice accumulates on optics with loss of signal at the detector, ice is
released after decontamination (cooler switch-off) The variation of position of ice maximum is due to variation of ice layer
thickness that can introduce other effects (e.g., ice scattering)
Ice effectsIce effects
-20
0
20
40
60
80
100
120
140
160
Nov-01 Dec-02 Jan-04 Feb-05 Mar-06 Apr-07 Jun-08 Jul-09
Ga
in v
aria
tio
n b
and
A (
%)
750
800
850
900
950
Wa
ven
um
be
r (cm
-1)
Max gain change in band A
Spectral position of Max (cm-1)
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Intro
Calibration
Ice effects
Summary
What’s next
slide 10
Rate of gain variationRate of gain variation The requirement of 1% increase/week is fulfilled (dashed line) We observe an overall decrease of outgassing along the mission. We observe the very contaminated period of Jan – Jun 2005, due to the
fact that decontamination was not planned during Feb – Dec 2004
Ice effectsIce effects
0
0.2
0.4
0.6
0 500 1000 1500 2000 2500
Days after launch
Max
ch
ang
e o
f g
ain
in
ban
d A
no
rma
lize
d b
y t
ime
(%
/ d
ays
)
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Intro
Calibration
Ice effects
Summary
What’s next
slide 11
Gain and NESRGain and NESR The NESR of the scene is defined as the standard deviation of the
measured single sweep spectral radiance taken over N measurements Gain and NESR variations are linearly correlated and similarly degraded
by ice contamination (loss of transmission)
Ice effectsIce effects
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Intro
Calibration
Ice effects
Summary
What’s next
slide 12
Gain and NESR variationGain and NESR variation NESR variation is linearly correlated to gain
Ice effectsIce effects
-20
0
20
40
60
80
100
120
140
160
Nov-01 Dec-02 Jan-04 Feb-05 Mar-06 Apr-07 Jun-08 Jul-09
Re
lati
ve
va
ria
tio
n w
ith
re
sp
ec
t to
re
fere
nc
e (
%)
Max of Gain variation in band A
Max of NESR variation at 70 km in band A
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Intro
Calibration
Ice effects
Summary
What’s next
slide 13
Ice effects on L2 precisionIce effects on L2 precision Precision is proportional to NESR NESR varies due to ice
contamination, but it is also slightly dependent on signal higher radiances means higher NESR
Precision (random error due to noise) on VMR retrieval is inversely proportional to Temp (Planck function) Higher Temp Stronger signal Better precision
The impact of these two factors (ice and atmospheric temperature) on the time variation of L2 precision is complex (see C. Piccolo and A. Dudhia, ACP, 7, 1915–1923, 2007): In general L2 precision degrades proportionally to ice contamination In case of weak species the L2 precision is critically degraded by
increasing NESR In case of large seasonal variation of atmospheric temperature (polar
region) L2 precision is more driven by variation of temperature Furthermore ice contamination impacts directly accuracy of profiles:
An error in the gain function of 1% directly translates into a systematic error of 1% in the calibrated spectra and then in the profiles
Ice effectsIce effects
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Intro
Calibration
Ice effects
Summary
What’s next
slide 14
Ice in other ENVISAT instruments: Ice in other ENVISAT instruments: AATSR and SCIAMACHYAATSR and SCIAMACHY
Ice was also seen on other ENVISAT instruments, AATSR and SCIAMACHY
It may be that outgassing from other parts of ENVISAT lead to increased water vapor pressure around the satellite, this water vapor may reach the MIPAS detector unit
Ice effectsIce effectsSignal loss and ice deposition rate on AATSR
Courtesy of VEGA Courtesy of SOST-IFE
Signal loss on SCIAMACHY channel 8
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Intro
Calibration
Ice effects
Summary
What’s next
slide 15
Summary and lessons learnedSummary and lessons learned Water is trapped on-ground in some parts of the platform (e.g., MLI) and it
evaporates in flight (outgassing) forming ice around the coldest parts of the ENVISAT satellite, in particular IR (cold) sensors such as MIPAS, AATSR and SCIAMACHY IR channels
Ice formation determines loss of signal at the detector Outgassing is increasing with Temp during hottest period of the year Outgassing is decreasing along the mission since contaminants are
progressively removed from the instrument Periodic decontaminations should be performed, in order to avoid that the
decrease of signal-to-noise ratio impacts products quality The most critical part of the mission is the first year, when very strong
contamination was seen in all ENVISAT IR sensors Similar issues were also found during operations of other IR sensors in
different platform (e.g., IASI and ACE)
SummarySummary
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Intro
Calibration
Ice effects
Summary
What’s next
slide 16
MIPAS mission extensionMIPAS mission extension The inclination control will be switched-off starting from 2011 in order to
minimize the fuel consumption. We will loose the repeat orbit track away from the equator and a drifting Mean Local Solar Time (MLST)
Since 2011 the altitude will be lowered by 25 km and controlled, while the MLST will be left drifting until end of the mission (possibly 2014)
No showstoppers have been found for MIPAS (instrument and processing), however some care should be taken in order to avoid sun light entering the ESU/ASU
What’s nextWhat’s next
EGU 2009Vienna
19 – 24 Apr 2009
Ice on IR Ice on IR sensors: sensors:
MIPAS caseMIPAS case
Intro
Calibration
Ice effects
Summary
What’s next
slide 17
Thank you for your attention !
AcknowledgmentM. Birk (DLR), G. Davies (VEGA), A. Dehn (Serco), A. Dudhia (Oxford
University)
Questions /
Answers
Questions /
Answers