This document summarizes an analysis of interference to spaceborne microwave radiometers operating in the 6-7 GHz band from downlinks of mobile satellite systems. It finds that interference exceeds acceptable levels in some cases, particularly when there is specular reflection from the ocean surface. The analysis is the first to quantify interference levels in ocean areas. Protection of the 6-7 GHz band for passive sensing is important but current radio regulations do not provide adequate protection.

1. IGARSS2011 Session:Frequency Allocation for Remote Sensing and RFI Mitigation for Microwave Radiometry PROTECTION OF 6-7GHZ BAND SPACEBORNE MICROWAVE RADIOMETERFROM INTERFERENCES TO DERIVE SEA SURFACE TEMPERATURE ANDOTHERS July 29,2011 KorehiroMAEDA (the University of Tokyo), Akira SHIBATA(JAXA), Keiji IMAOKA(JAXA)

2. Contents 1.INTRODUCTION 2.INTERFERENCE SOURCES Direct interference and interference scattered in ocean 3.INTERFERENCE ANALYSIS Interference analysis from mobile satellites to spaceborne microwave radiometer in ocean area The first results in the world. 4. CONCLUSION 2

3. 1.Introduction (1/2) There are several spectrum issues related with remote sensing. Some issues have been resolved thorough WRC, study groups SG7, Working Party of WP7C of ITU-R in collaboration with various space agencies and remote sensing community such as GRSS FARS (Frequency allocation for Remote Sensing). These issues cover not only spaceborne active sensor such as cloud radar, precipitation radar and synthetic aperture radar but also spaceborne passive sensor such as microwave radiometer. Some issues such as protection of 6-7GHz microwave radiometer are still not resolved. Table 1 shows combination of channel to derive geophysical parameter. In this table, Radio Regulations (R.R. ) was modified in WRC-2000 for 18.6-18.8GHz and in WRC-2007 for 10.6-10.68GHz, 23.6-24GHz and 36-37GHz. Emission is prohibited by R.R.No.5.340 for 10.68-10.7GHz, 23.6-24GHz, 87.5-90.5GHz. 3

4. 4

5. 5

6. 1.Introduction (2/2) 6-7GHz microwave radiometer is very important and best to observe sea surface temperature and others through clouds. However, this band is not protected in Radio Regulations (R.R.) of ITU-R. Therefore various interference sources to 6-7GHz microwave radiometer are classified and introduced. Sharing analysis in land area is conducted [1]. Aircraft experiment was conducted to measure interference in Japan in 2006 [2]. In the ocean area, there is no analysis to date. In this paper, sharing analysis is shown for the first time in the world. 6

7. 2. INTERFERENCE SOURCES There are the following interference sources to spacebornemicrowave radiometer using 6-7 GHz: (1)Interference from radio ground system There are various interferences in the AMSR-E image as shown in Figures 1 and 2. (2)Scattered emission of down link of feeder link of a mobile satellite over the surface of ocean There are line-shape interferences in the AMSR-E image as shown in Figure 3. (3) direct radiation from mobile satellite to horn of microwave radiometer via edge of main reflector. There is interference of part of main dish shape in the AMSR-E image as shown in Figure 4. (4)Interference to cold sky mirror for calibration. Calibration accuracy using cold sky mirror is degraded. 7

8. 2. INTERFERENCE SOURCES (2/2) These interferences cause error in extraction of geophysical parameter such as sea surface temperature, sea surface wind and others. Importance of 6-7GHz in measurement of sea surface temperature and sea surface wind are shown in Ref.[3] and [4]. 8

9. 9

10. 10

11. 11

12. 12

13. Radio Regulations No.5.458 6-7GHz band is not protected in R.R. No.5.458 which shows that in the band 6 425-7 075 MHz, passive microwave sensor measurements are carried out over the oceans. In the band 7 075-7 250 MHz, passive microwave sensor measurements are carried out. Administrations should bear in mind the needs of the Earth exploration-satellite (passive) and space research (passive) services in their future planning of the bands 6 425-7 025 MHz and 7 075- 7 250 MHz. Modifications of Radio Regulation may be needed in the future. JAXA is planning to launch AMSR-2 mounted on GCOM-W in November, 2011 which has additional band 7.3GHz (350MHz) to 6.925 GHz (350MHz) band in order to select channel with lower interference. 13

14. 3. INTERFERENCE ANALYSIS (1/4) 3.1. Technical characteristics Values of parameter of a mobile satellite and spaceborne microwave radiometer and a mobile satellite are shown in Table 2 and 3. 14

15. 15

16. 16

17. 17

18. 18

19. 19

20. 3.2. Interference analysis (2/4) Typical interference in the ocean is caused by scattering at surface of ocean. Interference analysis is conducted by applying radar equations and using Table 2 and 3. Dependence of scattering coefficients on incidence angle are shown in the following figures. 20

21. 21 Scattering coefficients (dB)

22. 22 Scattering coefficients (dB)

23. 23 Receiving power Pr of a spaceborne microwave radiometer is given by the following equations:

24. 3.2. Interference analysis (3/4) Back scattering radar cross section of surface of ocean is obtained in Ref.[5]. This can be converted to forward scattering as shown in Ref.[6]. Forward scattering coefficients is assumed to be a function of a single variable, the off-specular angle, where off-specular angle is the angle between the direction of specular reflection and the direction in which the energy is scattered to the receiver of microwave radiometer. 24

25. 3.2. Interference analysis (4/4) In this case, the scattering coefficients is circularly symmetric around the direction of specular angle. When incidence angle at the earth is 55 degree and specular reflection occurs, this is worst case. In this case, Pt is calculated as shown in Table 4. According to Rec.ITU-R RS.1029-2[8], interference level -166dBW (Reference bandwidth 200MHz) should not exceeded for more than 0.1 percentage of sensor viewing area. In the case of specular reflection, it was found that protection level was exceeded by about 33dB for AMSR-E and AMSR2. 25

26. 26

27. 27

28. 4. CONCLUSION Various interference sources to a 6-7GHz spaceborne microwave radiometer are classified and introduced. These interferences cause degradation of accuracy of sea surface temperature, sea surface wind and others. In particular, interferences from scattering of downlink from mobile satellites to gateways at the ocean are analyzed for the first time in the world. It was found that interference level exceeds protection level by about 33dB in the specular reflection case. Dynamic analysis will be needed to measure interference time percentage. We hope that community of GRSS will make efforts to act to protect 6-7GHz spaceborne microwave band 28

29. ACKNOWLEDGEMENT The authors would like to thank member of GCOM, JAXA. 29

30. REFERENCES [1] Korehiro Maeda, “Utilities of SpaceborneMicrowave Radiometer and its Protection-sharing studies between AMSR and point-to-point fixed service stations,”IEICE Technical report SANE2004-113,pp.61-66, March, 2005. [2] KeijiImaoka, Yasuhiro Fujimoto, Yoriko Arai, Akira Shibata,ShinichiMorokuma, and Yoshio Sasaki “Radio-frequency interference signals in the AMSR and aircraft C-band measurements,” proceedings of IGARSS2006,pp.2297-2300, 2006. [3]Akira Shibata, ”Necessity of frequency 6GHz for observing sea surface temperature, IEICE Technical Report SANE2010-37 pp.123-126, 2010. [4]Akira Shibata,”A wind speed retrieval algorithm by combining 6 and 10GHz data from Advanced Microwave Scanning Radiometer: Wind Speed inside Hurricanes,”Journalof Oceangraphy, vol.62, pp.351-359,2006. [5]G.R.Valenzuela,”Theories for the interaction of electromagnetic and oceanic waves-a review,”Boundary-Layer Meteorol, vol.13.pp.61-85,1978. 30

31. REFERENCES [6] Rec.ITU-R RS,1449,”Feasibility of sharing between the FSS (space-to-Earth) and the earth exploration-satellite (passive) and space research (passive) services in the band 18.6-18.8GHz” 2000.1449 [7]Rec.ITU-R RS.1029-2 “Interference criteria for satellite passive remote sensing,”2003. [8] K.Maeda and Y.Azuma, ”Outline of SAR-580 data processing method in Japan, “ IGARSS’86 Symposium, pp.1413-1418, Sept., 1986. [9]K.Maeda, M.Kojima and Y.Azuma, ”Some results of MOS-1 airborne verification experiment-MESSR,” IGARSS ’ 86 Symposium, pp.15-20,Sept.,1986. [10]K.Maeda, M.Kojima and Y.Azuma,”Some results of a MOS-1 Airborne Verification Experiment –Multispectral Electronic Self-Scanning Radiometer (MESSR),” IEEE Transactions on Geoscienceand Remote Sensing Vol.GE-25, No.6, pp.788-795,Nov.1987. 31

32. REFERENCES [11]K.Maeda, H.Wakabayshiand H.Sato,”Some results of MOS-1 airborne verification experiment-MSR (Microwave Scanning Radiometer),” Proceeding of IGARSS’87 Symposium, pp.1073-1078, May 1987. [12]K.Maeda and Y.Azuma, ”Results on processing and evaluation of SAR-580 data in Japan, “Canadian Journal of Remote Sensing Vol.13, No.1, pp.11-18, July 1987. [13]K.Maeda,M.Kojima and Y.Azuma, “Geometric and radiometric performance evaluation methods for marine observation satellite-1(MOS-1) verification program(MVP),”ActaAstronautica, Vol.15, No.6/7, pp.297-304, Pergamon Journals, 1987. [14] K.Maeda,H.Wakabayashi,K.Tasaki,M.Shimadaand H.Satoh,”Verification results of MOS-1 MESSR data,”Proceedingsof IGARSS ‘ 88, pp.271-274, 1988. [15]K.Maeda, H.Wakabayashi, K.Tasaki and H.Sato,”Early Verification Results for MOS-1 VTIR data, , Proceedings of 16th ISTS , pp.2197-2204, 1988, 32

33. REFERENCES [16] K.Maeda and H.Satoh,”Application of MOS-1 data to earth environment monitoring and future global change monitoring system,” Proceedings of 17 th ISTS, pp.1995-2001, 1990. [17] K.Maeda, M.Nakai and O.Ryuguji,”ERS-1/ERS-1 verification program and future verification program,” Adv.SpaceRes.Vol.12, No.7, COSPAR, pp.(7)327-(7)331, 1992 [18] K.Maeda and H.Maejima, ”Development of ISY environmental data sets,” Proceedings of 18 th ISTS, pp.2015-2020, 1992. [19] K.Maeda and H.Maejima, “Development of data sets for the ISY sea surface temperature,”, European ISY Conference, March, 1992. [20]K.Maeda, H.Maejima, M.Shimada and T.Tanaka., ”MOS-1/MOS-1b/ERS-1/JERS-1 data sets of sea surface temperature and polar ice extent for ISY,” Adv.Space Res.Vol.14, No.3,COSPAR, pp(3)167-(3)176, 1994. 33

34. REFERENCES [21] K.Maeda and O.Ryuguji, ”Japanese contribution to development of earth environment monitoring system by using satellites,” Space technol.Vol.12, No.1 , Pergamon Press, pp.83-90, 1992. [22] K.Maeda, “Disaster monitoring using multi-satellite system, Proceedings of 19 th ISTS, 1994. [23]K.Maeda, Y.Iida and T.Manabe,”Protection of Spaceborne and Terrestrial Passive Sensors to Observe Trace Gasses from 200 to 700GHz,” Proceedings of IEEE IGARSS Symposium,pp.2467-2470, 2000. [24] K.Maeda, K.Ohishi and F.Hosonuma, ”Outline of spaceborne sub-millimeter wave sounder with superconductivity,” 20 th International Conference on infrared and millimeter waves Dec.,1995. 34