ENVISAT RA-2/MWR CCVT Plenary Meeting – 25-27/03/2003 ERS-2 RA/MWR status Pierre Féménias ESA/ESRIN

ENVISAT RA-2/MWR CCVT Plenary Meeting – 25-27/03/2003

ERS-2 RA/MWR status

Pierre FéméniasESA/ESRIN


ERS-2 Mission

– All services provided by ERS-2 remain fully operational. All LBR instruments are operated on a global basis.

– The Instrument Data Handling and Transmission (IDHT) is also working nominally except for the chain of the Tape Recorder B that suffered an anomaly on December 20, 2002.

– The Chain of the Tape Recorder A is continuously used. – Investigation to locate the origin of the failure on recorder B

is on-going, in spite the difficulties to obtain detailed technical information and support from the tape recorder manufacturer


ERS-2 Platform Operations

– The AOCS is operating in Zero-Gyro Mode (ZGM) for the Fine Modes (ZGM-FM) and in Mono-Gyro Mode for the Coarse Modes (MGM-CM) (i.e. for the Safe Mode Exit and the Out Of Plane manoeuvres)

– The pointing performance of the ZGM-FM remains well within the requirements for the ERS mission

– The performance of the Digital Earth Sensor, Digital Sun Sensor, Reaction Wheels, Magneto Torque and thrusters is outstanding


ERS-2 Platform Operations

– Performance of Gyro #4 (used for the Safe Mode) is excellent, while the performance of Gyro #6 (used for the Coarse Modes) and Gyro #3, used as a back-up of #6, may start degrading after continuous use over several days

– The Extended MGM (E-MGM) will permit the use of the Gyros #3 and #4 in Mono Gyro Mode for the Coarse Modes and Orbit Control Manoeuvres

– The software for the E-MGM Coarse Mode has been fully validated and will be up linked once E-MGM operation becomes necessary.

– The development of the E-MGM for the Out of Plane Manoeuvres has started on January 2003 and is on schedule for delivery by end of July.


ERS-2 Subsystems

– Power Subsystem • The solar array delivers a level of power higher than the

minimum required. Panel degradation is much smaller than specified

• The batteries are performing the charge/discharge cycles almost at the same levels as after launch

– Thermal Subsystem• Average and variation ranges of temperatures of each

element of the spacecraft remain stable since launch. • No ageing in the walls’ coating has been verified

– Fuel Budget• The total mass available permits to envisage the long-

term operation plus the final de-orbiting of the satellite


ERS-2 RA Instrument

RA background mission scheduled according to ocean-land transitions:

• Ocean mode over ocean zones all the time• Ice mode over land zones and Antarctica all the time

• From February 13, 2002, I.e. from orbit 35644, the Great Lakes are now tracked in Ocean mode


ERS-2 RA Instrument


ERS-2 RA Instrument

– Daily extraction of RA ERAC raw data (10 min) for mispointing monitoring

– Raw data availability over the last 7 months > 98%. Most of

the data outage due to GS operational problems, instrument

unavailability due to Leonid Operations, IDHT unavailability,

etc

– RA Acquisition percentage over Ocean < 2%

– No sensible degradation is detected in any of its modules

– The RA instrument performs nominally




ERS RA Wind & Wave• A large number of outliers (RA values higher than model) in the

scatter plot for the wind speed in the Southern Hemisphere. Most of the outliers can be attributed to the DES sun-blinding phenomenon

• Apart from that, the quality of Altimeter data is as good as they used to be

• Clear tendency for improved agreement between RA and model data in the Northern Hemisphere after 18 January 2003 (there was no RA on that day)

• It is not clear yet if the ECMWF model changes (on the 13th. of the month) or a change in the RA behaviour are responsible for this improvement

• Note: ECMWF atmospheric and wave models have been changed to CY25R3 (en.) on 13 January 2003 (since 18: 00 UTC). ERS- 2 SAR data are assimilated by the wave model. Other atmospheric changes have been introduced as well


ERS-2 RA Range Long Term Monitoring

Mean of the difference (Altimeter sea surface height – OSU95 mean sea surface height) versus ERS-2 cycle number. (OPR data products)



Standard deviation of the difference (Altimeter sea surface height – OSU95 mean sea surface height) versus ERS-2 cycle number



Mean of Bent ionospheric correction (in mm) versus ERS-2 cycle number



• A trend is observed on SSH-MSS long term monitoring, with particularly high changes since cycle 50 (beginning of year 2000)

• Such changes cannot be explained by mispointing problems alone • Orbit errors could also partly explain some part of these variations • Main contribution seems to come from the BENT correction, which

poorly retrieves large variations of the ionosphere correction during periods of high solar activity

• A more complete study about the impact of the ionosphere correction will be carried out in 2003, using GIM (GPS Ionospheric Maps, http://iono.jpl.nasa.gov/gim.html) corrections, if available


ERS-2 Platform PointingOff-nadir angle overall trend (Asc and Desc orbit from [0º,35º] latitude

north)


ERS-2 Platform Pointing

Along-the-orbit mispointing squared behavior– Periodical with orbital period

– Lower values recorded over zones close to the equator (Asc & Desc)

– Higher values recorded over zones close to the south and the north poles

the last only during winter Season:

Sun Blinding Effect !(period from ~Nov to Feb)


ERS-2 Orbit

• Orbit Maintenance Performance: Control Dead Band

Distance of the actual orbit respect to the theoretical one:

– Between 50 and 30 latitude north during descending passes and between 50 and 30 latitude south for ascending passes: ±1 Km

– Outside those areas: around ±2 Km


ERS OPR Reprocessing

• ERS OPR Level 2 product

– Reprocessing of ERS-1 Phase C in OPR V6 completed in early January 2002

– Reprocessing of remaining phases approved by ERS SG (11/02)

– Squared off-nadir angle squared at 1Hz and a smoothed value evaluated using a 30 second sliding window available in OPR02 since cycle 60 (01/01)

ERS-1 Phase A (Jul 91 - Dec 91) Com. Phase 6 monthsERS-1 Phase B (Dec 91 - Mar 92) Ice 4 monthsERS-1 Phase C (Apr 92 - Dec 93) Multi-disciplinary 21 monthsERS-1 Phase D (Jan 94 - Mar 94) Ice 3 monthsERS-1 Phase E/F (Apr 94 - Mar 95) Geodetic 11 months


ERS-2 MWR Instrument



MWR Gain long term stabilityover ~6 years- Gain very stable- 24GHz channel ok, despitethe June ’96 anomaly



• A long term survey of Brightness Temperatures (BT) over the coldest points on ocean revealed a trend with time (-1.5K over 6 years) of channel 24 GHz

• The trend has consequences on the tropospheric correction, which decreases with time.

• This effect is maximum for coldest points, and is lower at mid values of the tropospheric correction

• A correction on the 24 GHz BT, depending on the time and on the BT value, is proposed. (http://earth.esa.int/pcs/ers/mwr/articles/ )



Mean and Std Dev of the coldest BTs over Ocean

(lower than a given threshold)



The correction proposed for this drift is the following :

TB23.8corrected_for_the_gain_drop_and_from_the_TBs_drift = TB23.8corrected_for_the_gain_drop + corr(t,TB23.8corrected_for_the_gain_drop)

With :

corr(t, TB23.8corrected_for_the_gain_drop) = 0 for t <= 1.18

corr(t, TB23.8corrected_for_the_gain_drop)= (a1*t+a2)* TB23.8corrected_for_the_gain_drop + (b1*t+b2) for t > 1.18

a1=-0.001521 b1=0.4564

a2=0.001795 b2=-0.5386

t the elapsed time in decimal year since ERS2 launch.



Correction Validation

• Long-term survey of the 23.8

GHz BTs after applying the

proposed correction

• The drift has been completely

corrected

Documents

ENVISAT RA-2/MWR CCVT Plenary Meeting – 25-27/03/2003 ERS-2 RA/MWR status Pierre Féménias ESA/ESRIN