CGMS-43-ISRO-WP-03, version-1, CGMS WGIII May 2015 Coordination Group for Meteorological Satellites - CGMS ROSA Data Processing at ISRO Presented to CGMS-43 WGIII, agenda item 2.2 Slide: 1

CGMS-43-ISRO-WP-03, version-1, CGMS WGIII May 2015 Coordination Group for Meteorological Satellites - CGMS Content 1 Radio occultation 1.1ROSA and GPS-ROS (ref. CGMS-42 action WGIII/ ) ISRO 1.2RO visiting scientist – follow-up and current status ISRO/EUM 1.3OCEANSAT2-ROSA statusISRO 1.4Current activities in ROSAISRO

CGMS-43-ISRO-WP-03, version-1, CGMS WGIII May 2015 Coordination Group for Meteorological Satellites - CGMS ROSA and GPS-ROS Reference CGMS-42 action WGIII/ Description ISRO to report at CGMS-43 on its progress on radio-occultation processing of ROSA on Oceansat-2 and Megha-Tropiques, and on the possibility of near-real time access to ROSA data acquired at a high latitude station such as Svalbard. Data processing software currently resides in NRSC, Hyderabad for O2-ROSA ( as only 4 dumps/day ). To get near real time data, scheme followed for O2-SCAT needs to be followed for O2-ROSA. Data processing software for MT-ROSA currently resides at ISSDC, Bangalore and data product is being hosted in MOSDAC, Ahmedabad. In CGMS-43 a technical paper/presentation towards the progress of the ROSA processing will be presented.

CGMS-43-ISRO-WP-03, version-1, CGMS WGIII May 2015 Coordination Group for Meteorological Satellites - CGMS RO visiting scientist – follow-up  Generated few days (i.e May 2013) MT-ROSA Level-1d products using, 1.Raw Bending Angles ( without use of climatology) 2.Retrieval algorithm is based on Geometric Optics (GO) only. and provided it to EUMETSAT for feedback. 3. Extrapolated L2 bending angles in lower atmosphere. (April 2015) Current status of “ISRO-EUMETSAT assessment on MT ROSA Data” Assessment: The number of failures has decreased from 23.6% to 8.9%. More data in altitude range from 3-20km, but still not what is expected. Standard deviations also much larger in mid troposphere now (GO processing limitation). Bias and standard deviations still far off from other RO instrument, in particular above about 16km. Number of occultations actually slightly less than before. Flag to identify event as rising and setting. Need to work more on L2 data in lower troposphere.

CGMS-43-ISRO-WP-03, version-1, CGMS WGIII May 2015 Coordination Group for Meteorological Satellites - CGMS Analyzed one month O2-ROSA raw data after onboard uploading of software patch by instrument provider TAS-I, Italy and evaluated raw data in terms of signal tracking and no. of occultation events. Product Quantity Improvement : 45 % to 65 % Oceansat-2 ROSA status L2 Signal Availability Geometric Impact Parameter (GIP) TotalGIP < 0 kmGIP < 10 kmGIP < 25 kmGIP > 25 km Rising (2.6%)121 ( 6.4%)369 ( 19.6%)1513 ( 80.4%)  2-6 Sept 2013 & 5-9 Jan 2014 ( 283 events / day ) ( 142 products / day ) - (Before Patch Update) Rising ( 4.2%)212 ( 10.5%)476 ( 23.6%)1536 ( 76.3%)  June 2014 & May 2014 ( 231 events / day ) ( 170 products / day ) – (After Patch Update-May 2014) Rising ( 6.0%)225 ( 15.0%)498 ( 32.0%)1038( 68.0%)  December 2014 ( 281 events / day ) ( 193 products / day ) – (After Patch Update-December 2014)

CGMS-43-ISRO-WP-03, version-1, CGMS WGIII May 2015 Coordination Group for Meteorological Satellites - CGMS Current activities in ROSA L2 data analysis L2 Tracking Issues: Analysis has been carried out based on Geometric Impact Parameter (GIP) and low level raw data 1-12 May 2013 ( 486 events / day ) TotalL2 data lossL1 & L2 High rate (50 Hz) data loss (21.0 %)911 (15 %) 1 April – 15 May 2013: L2 Signal Availability Geometric Impact Parameter (GIP) TotalGIP < 0 kmGIP < 10 kmGIP < 25 kmGIP > 25 km Rising ( 3.08 %)978 ( 9.79 %)3188 ( %)6796 ( %) Setting ( 73.8 %)9017 ( %)9126 ( %)1307 ( %) All ( %)9995 ( %)12314 ( %)8103 ( %) Need to work more on L2 data (50Hz) as a part of pre-processing. (Based on Feedback from EUMETSAT) (ongoing)

CGMS-43-ISRO-WP-03, version-1, CGMS WGIII May 2015 Coordination Group for Meteorological Satellites - CGMS  New changes has been introduced in the MT-ROSA software : Sliding polynomial regression (0.5 sec window, 3 rd order) to filter raw L1 and L2 excess phases. Fourier filtering with Gaussian window to filter L1 and L2 Doppler. Dynamic L2 signals cut off based on L1-L2 Doppler (1.5 Hz) quality. Fourier filtering to filter L1 bending angles with 0.5 sec window. Optimal linear combination of L1 and L2 bending angles for ionospheric correction. Extrapolating bending angle below dynamic L2 QC(Quality check) height based on linear fit to L1-L2 bending angles.  As a part of action close out on the previous assessment by EUMETSAT : Flag in Level 1d.nc product to define event as setting and rising. (closed) Analysing the strong noise in higher altitude about 30 km, POD effect (ongoing) Merging Wave Optics with improved Geometric Optics approach and further testing (ongoing) Preliminary results : Inter-sensor comparison with COSMIC ( ) is carried out by doing above changes. Changes in the latest software and results

CGMS-43-ISRO-WP-03, version-1, CGMS WGIII May 2015 Coordination Group for Meteorological Satellites - CGMS MT-ROSA Global Distribution (1-12 May 2013) MT ROSA – Version 5 (Previous software) (2650 products) MT ROSA – Version 6 (latest software) (3062 products)

CGMS-43-ISRO-WP-03, version-1, CGMS WGIII May 2015 Coordination Group for Meteorological Satellites - CGMS Conclusions on the basis of latest software  On the basis of latest software, we can conclude following: Comparison with COSMIC reprocessed data ( ) shows a considerable improvement in terms of relative bias in bending angle between km. Standard deviation is a slightly more as compared to previous software. Need to look more into POD aspect and also on raw inputs e.g. L1 and L2 carrier phases. Though number of collocated events are more from 18 to 45 km, but below that penetration has degraded, probably because of the L1 and L2 cut-offs has shifted upwards due to less filtering. Percentage increase in the number of products is 7% as compared to previous delivery to EUMESAT. Need to introduce wave optics where Geometric optics poses limitations esp. in lower troposphere. Once the changes are finalized and evaluation is done on more number of datasets, we would like to share a sample data with EUMETSAT for further validation with ECMWF. The changes introduced will be implemented in O2-ROSA post finalization in MT-ROSA.

CGMS-43-ISRO-WP-03, version-1, CGMS WGIII May 2015 Coordination Group for Meteorological Satellites - CGMS Slide: 10 MT-ROSA: Quality Status of geophysical parameters Improvement in relative bias & RMSD between 8-25km for Refractivity. Significant error persisting above 25km (Cause of concern for Physical retrieval algorithm). Below 8km, error in refractivity within 5-6%. Temperature errors are reasonable up to 20km. Above 20km, RMSD is significantly large (Reason being the existing large RMSD of refractivity). Jump in bias around 20km (also seen in refractivity) require proper merging between WO & GO. Relative Bias & RMSD of Refractivity & Temperature w.r.t COSMIC (collocation window: Delta(x)=100km; Delta(t)= 2hrs)

CGMS-43-ISRO-WP-03, version-1, CGMS WGIII May 2015 Coordination Group for Meteorological Satellites - CGMS Slide: 11 Bias and RMSD of Refractivity w.r.t. collocated NCEP analyses. Previous version (left fig.) and current version (right fig.) compared for the common data period: Apr Improvement in relative bias & RMSD above 15km. Error trend is similar below 15km in both the versions.

CGMS-43-ISRO-WP-03, version-1, CGMS WGIII May 2015 Coordination Group for Meteorological Satellites - CGMS Bias and RMSD of Temperature w.r.t. collocated NCEP analyses. Previous version (left fig.) and current version (right fig.) compared for the common data period: Apr Bias & RMSD show significant improvement at all levels, especially above 15km and below 10km. Standard deviation up to 5K. Will improve further with accurate refractivity.

CGMS-43-ISRO-WP-03, version-1, CGMS WGIII May 2015 Coordination Group for Meteorological Satellites - CGMS Slide: 13 Summary  Both bias and RMSD show significant improvement in refractivity between 8-25km.  Corresponding improvement seen in temperature error.  Higher errors persist above 25km causing large retrieval errors in geophysical parameters at these levels.  Systematic errors in refractivity suggest improved algorithms are needed.  Trade-off between- more occultation events-penetration vis-a’-vis quality of profiles, to be treated on merits, as data sparse region and for critical applications, strict quality regimes might need to be relaxed. This may call for dual data processing regimes.