Korean Journal of Remote Sensing, Vol.27, No.2, 2011, pp.163~170 Change of Refractive Index of Air in X-band due to Atmospheric Humidity, Temperature and Pressure measured by GB-SAR Interferometry Jae-Hee Lee*, **, Hoonyol Lee*, Seong-Jun Cho**, Nak-Hoon Sung** and Kwang-Eun Kim** *Department of Geophysics, Kangwon National University **Mineral Resources Research Division, Korea Institute of Geoscience and Mineral Resources Abstract : In this paper, we analyzed the phase change of 5-triangular trihedral corner reflectors by using X-band Ground-Based Synthetic Aperture Radar (GB-SAR) system. Each reflector was set as a stationary target at a different distance from the system. We obtained total 123 full-polarization images during 40 hours continuously at 20 minute interval. Results of SAR interferometric analysis showed phase changes of maximum 2 radians and followed similar pattern with atmospheric data. Through a GB-SAR phase formula that includes refractive index in the air, we performed regression analysis for refractive index as a function of atmospheric humidity, temperature and pressure. As a result, refractive index of air in X-band showed relatively high coefficient of determination with humidity and temperature (0.72 and 0.76 on average, respectively) but not so with pressure (0.34). The refractive index of air in X-band changed by 3.14 10 _ 5 during the measuring time with a humidity range of 50% ~ 90% and a temperature range of -1 ~ 9. We expect that a total expression of refractive index of air including humidity, temperature and pressure can be calculated when more extensive data would be collected at various atmospheric conditions. Key Words : synthetic aperture radar, interferometry, humidity, temperature, pressure, refractive index hoonyol@kangwon.ac.kr 163
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Change of Refractive Index of Air in X-band due to Atmospheric Humidity, Temperature and Pressure measured by GB-SAR Interferometry Fig. 1. Photo of the experiment location. 5 red triangles indicate triangular trihedral corner reflectors that used as stationary targets. Table 1. Parameters for the GB-SAR Experiment Date and Time 5 PM Feb. 6, 2009~9 AM Feb. 8, 2009 (40 hours) Humidity 50.4~90.1 % Atmosphere Temperature -1.2~9.0 Pressure 1020.9~1026.2 hpa Center frequency 9.65 GHz Bandwidth 600 MHz Range Polarization HH, VV, HV, VH Range sampling 1601 Power 37 dbm Azimuth scan length 5 m Azimuth Azimuth step 5 cm Azimuth sampling 101 165
Korean Journal of Remote Sensing, Vol.27, No.2, 2011 (a) HH-polarization (b) VV-polarization (c) VH-polarization Fig. 2. GB-SAR amplitude images. (d) HV-polarization (a) HH-polarization (b) VV-polarization (c) VH-polarization (d) HV-polarization Fig. 3. Phase changes relative to the first image in (a) HH, (b) VV, (c) VH and (d) HV during the experiment. 166
Change of Refractive Index of Air in X-band due to Atmospheric Humidity, Temperature and Pressure measured by GB-SAR Interferometry f = _ 4p nr (1) l l R n Df = _ 4p DnR (2) l (a) (b) (c) Fig. 4. Atmospheric conditions during the GB-SAR experiment. (a) Atmospheric humidity, (b) Temperature and (c) Pressure. 167
Korean Journal of Remote Sensing, Vol.27, No.2, 2011 Fig. 5. Changes of refractive index of air in X-band as a function of humidity, temperature and pressure at various channels. Dn = _ l Df (3) 4pR Dn 168
Change of Refractive Index of Air in X-band due to Atmospheric Humidity, Temperature and Pressure measured by GB-SAR Interferometry Table 2. Results of regression and coefficients of determination (R 2 ) between refractive index of air in X-band and humidity (h), temperature (T) and pressure (P). Dn = ah + b, [50.4 h 90.1%] Dn = ct + d, [ _ 1.2 T 9.0 ] Dn = ep + f, [1020.9 P 1026.2hPa] humidity (h) temperature (T) pressure (P) a 10 7 b 10 5 R 2 c 10 6 d 10 5 R 2 e 10 6 f 10 3 R 2 HH 5.497-2.930 0.81-2.171 1.867 0.83 3.505-3.574 0.39 VV 5.452-2.890 0.76-2.187 1.880 0.80 3.258-3.321 0.31 VH 5.364-3.052 0.67-2.159 1.640 0.71 3.314-3.381 0.30 HV 5.464-3.302 0.67-2.202 1.478 0.72 3.514-3.588 0.33 Dn = ah + b, [50.4 h 90.1%] Dn = ct + d, [ _ 1.2 T 9.0 ] (4) Dn = ep + f, [1020.9 P 1026.2hPa] a b c d e f h T P 169
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