1. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 Elevation and Climatological Dependence of the SSI Capabilities to Discriminate Atmospheric Propagation Conditions Ada V. Bosisio 1, Ermanno Fionda 2, Piero Ciotti 3, Antonio Martellucci 4 1) CNR\IEIIT, Milano, Italy; bosisio@elet.Polimi.It 2) Fondazione Ugo Bordoni (FUB), Roma, Italy; efionda@fub.It 3) Dept. Of Elect. And Info. Eng., Univ. Of Laquila, Laquila, Italy; piero.ciotti@univaq.It 4) ESA-ESTEC, TEC-EEP, Noordwijk (NL); antonio.martellucci@esa.Int 1

2. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 2 Microwave Propagation Phenomena Key parameter: Frequency (f) O2, Water Vapor emissions: (Clear Sky) Cloud emissions: relevant at f > 15 GHz Rain events: relevant at f > 10 GHz Snow and Ice, not relevant below f = 30 GHz SCENARIO

3. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 MOTIVATION 3 Rain events can be source of strong scatter processes extremely severe for space communications at K/Q/W band 1.For satellite communications purposes, the knowledge in real time of rain events, in the volume of the operative beacon, could suggest the adoption of dynamic fading mitigation techniques to overcome the lost of signal quality 2.For Water Vapor and Cloud Liquid retrieval, the availability of a user-friendly tool (able to detect microwave radiometric observations affected by rain) is welcomed in case of massive measurements (radiometric-networks) or for analyzing large database

4. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 CANDIDATE INDICATOR (SSI) 4 Indicator should be generated from ground-based brightness temperature values T b (f) It could benefit from the different sensitivity of the microwave radiometric channels to the various atmospheric constituents Candidate: The Sky Status Indicator (SSI) issues from the ratio between available T b (f) @ 23.8, 31.4 GHz

5. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 OUTLINE 5 Sky Status Indicator –SSI features –SSI computation –Clear sky T b (f) and calibration check Sensitivity analysis on SSI coefficients (synthetic data) –elevation angle and site (climatology & latitude) dependence –erroneous calibration procedure and/or apparatus uncertainty Sensitivity analysis on SSI coefficients (measured data) –elevation angle dependence SSI classification results Final remarks

6. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 ASSUMPTIONS The ratio T 31 /T 23 of concurrent ground-based radiometric data depends on the thermodynamic state of the atmosphere. This ratio detects the status of the sky along the path as it neutralizes the contribution of the water vapor plateau (continuum) and of the dry gases by defining a modified brightness temperature T 31 value: The coefficient c 0 is frequency-, location-, and elevation-dependent. It is computed either from measurements or from simulation data. Specifically, c 0 is the intercept of the straight line that relates the couple (T31,T23) of values under clear sky condition 6 SSI FEATURES

7. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 SSI COMPUTATION 7 The key point is c 0 calculation, i.e. the identification of the linear fit between T 23 and T 31 under clear sky conditions from simulated T b (f): from measured T b (f): Forward RT RAOBs Tb(f),IWV, LWP

8. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 8 CLEAR SKY T B AND CALIBRATION CHECK

9. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 SENSITIVITY ANALYSIS ON SSI COEFFICIENTS RAOBs database + forward RT model including: – Rosenkranz absorption model (water vapor) – Mattioli et al. (cloud model) Classification criteria 3 sites (De Bilt, Roma, Milano) 5 elevation angles = 27.6°, 35.5°,40.2°, 69.6°, 90° 9 The sensitivity analysis aims at assessing the dependence of c i coefficients on the elevation angle and on the climatological region. INPUT

10. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 RAOBS and SIMULATED T b (f) DATABASE 10 Period# samplesLat, Long % clear sky conditions De Bilt2002 -20083618(52.1N,5.18E)29 Milano2002 -20086518(45.43N,9.28E)41 Roma2002 -20085984(41.65N,12.48E)50 Classification criteria according to the outcome of cloud liquid model Clear sky conditions: LWP <0.001 cm Cloudy sky conditions: 0.001< LWP< 0.07 cm

11. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 SENSITIVITY ANALYSIS ON SSI COEFFICIENTS 11 Observed variability @ 90° : 8% Climatology- latitude joint effect

12. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 NOISE AND IMPROPER CALIBRATION EFFECTS 12 T bn (f)=T b (f) + N (0, N is AWGN with = 0.5 K. It accounts for the instrument radiometric resolution. T bne (f)=T bn (f) ± i where i=1,2 K The bias reproduces measurements under improper calibration periods Robustness is evaluated on simulated T b (f)

13. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 NOISE AND IMPROPER CALIBRATION EFFECTS 13 Sensitivity due to ± 1 and ± 2 of about ±6% and ±12 %

14. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 EXPERIMENTAL FIELD IN CABAUW (NL) 14 Antenna beam parameters Frequency [GHz]15.322-3190 Side lobe level [dBc]<- 30 <- 40 Directivity [dB]28.433.233.0 HPBW [°]6.23.3 -3.73.0 ESA ATPROP RAOB 22 km

15. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 SENSITIVITY ANALYSIS ON SSI COEFFICIENT 15 the T 23 domain ranging from its minimum value to 50 K is divided in 200 bins for each bin the minimum T31 value is selected linear fit over the selected couples T 23 - T 31 discrepancy from 6% to 9% for c o and of about 1% for c 1

16. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 SSI PROBABILITY DENSITY FUNCTIONS 16

17. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 SSI CLASSIFICATION RESULTS: CABAUW(NL) 17 SSI range variability and boundary threshold values with respect to the clear, cloudy and rainy sky conditions. The SSI values are referred to brightness temperature values measured in Cabauw during 2009.

18. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 T B (15.3) AS POSSIBLE RAIN DETECTOR TOOL 18

19. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 T B (15.3) DURING RAIN EVENTS 19

20. VII Riunione annuale CeTeM-AIT – Bari – 4,5 Dicembre 2012 FINAL REMARKS: RESULTS AND OUTLOOK SSI has easy software implementation and online performance capability Clear/cloudy and cloudy/rainy sky conditions were discriminated by two SSI boundary threshold values: 0.39 (at equal to 90° and 69.6°) and 0.86 or 0.88 (at equal to 90° and 69.6°). A robustness analysis on SSI considering simulated T b AWGN with = 0.5 K and a bias of ±1 and ±2 K: – Sensitivity of about ±6% and ±12 % Precipitation prediction through plane parallel rain slab to extend classification criteria to rainy sky conditions Database of meteorological information such as rain gauges and/or radar data for experimental validation 20