Estimation of Semitransparent Cirrus Height from MOS-1/VTIR Data Abstract A method to estimate semitransparent cirrus height together with temperature from the observed data of the water vapor absorption channel (Chan. 2 : 6.0-7.0um) and window channel (Chan. 3 : 10.5-11.5 um) of VTIR (Visible and Thermal IR Radiometer) onboard MOS (Marine Observation Satellite)-1 is developed. The method is based on the radiative transfer model. In the derivation of the estimating formula following assumptions are made. (1) Scattering effect in the cirrus is neglegibly small in the spectra of these channels. (2) The temperature of cirrus and lower boundary (sea surface) is homogeneous in the area for computation. (3) The emissivity of the cirrus is equal in these spectra. (4) The temperature of the cirrus is equal to that of the ambient air. Under the above assumptions, radiance of Channel 2 (R 2) can be expressed in terms of the radiance of Channel 3 (R 3) as follows. R 2=aR 3+b, where a and b are determined through the least square method. Then the height of the cirrus can be decided through following procedures. (1) Compute radiances from the cirrus at the height of the initial guess for Channels 2 and 3. (2) Substitute the computed R 2 and R 3 into the above equation. If the equality doesn't hold adjust the initial guess height of the cirrus and repeat the procedure until the equality is reached. The height where the equality is satisfied is the cirrus height and the air temperature temperature. of that height is the cirrus In the computation of the radiative transfer equation, the upper air data provided weather prodiction group can be utilized. by the numerical Results of verifications indicates that there is a good correspondence between the height of cirrus estimated based on the proposed method and that obtained from the data of radiosoundings. by M. Tokuno, and K. Tsuchiya Remote Sensing and Image Research Center Chiba University, Yayoi-cho, Chiba city, Chiba, 260, Japan

Fig.2 Schematic representation of the calculation of cloud height by Eq. (14). Fig.3 The flow chart to calculate cirrus cloud height by the proposed model.

Fig. 7 Schematic representation for estimation of subsatellite points on earth. Fig. 8 Water vapor image at 10 : 00 LST on 28 Oct. 1987.

日 Table4 Same as Table3 except at the Grid Point (34.0N, 137. 0E) Fig.9 Same as Fig.8 except the infrared image. Table5 Table3 The Same Vertical Distribution of Tempera- tore, Relative Humidity and Ratio at the Grid Point(42.5N, at 09 LST as Table3 except at the Grid Point (24.5N, 138.5E) Mixing 138.OE) 28 on Oct. 1987. 地 域 で あ る 第3章 で 述 べ た ア ル ゴ リ ズ ム に よ り,こ れ ら4地 域 の 薄 い 巻 雲 域 の 温 度 と高 度 を 求 め る 4.1鉛 直 プ ロフ ァ イル 使 用 し た鉛 直 プ ロ フ ァ イル は,温 度,水 4.モ デ ル の 検 証 と結 果 い て は,1987年10月28日09時(日 使 用 した 衛 星 デ ー タ は,1987年10月28v10時(日 本 時 間)に 取 得 さ れ たMOS-1パ ス18のVTIRデ 作 成 の2.5 2.5 ー タ で 幾 何 学 的 補 正 及 び ラ ジ オ メ ト リ ッ ク補 正 後LCCに 地 図 投 影 され た レベ ル2の 域 はFig.8(チ ャ ネ ル2)及 デ ー タで あ る,検証 対 象 地 びFig.9(チ ャ ネ ル3)の 黒 枠 で 囲 ま れ た 領 域 で あ る そ れ ぞ れ 北 か らA,B,C, D地 域 と す る これ ら4地 域 は,可 地 上 実 況(A,B地 域0)み)よ 視,赤 外画 像及 び り薄 い 巻雲 と判 断 で き た N2O,エ 蒸 気量 に つ 本 時 間)の 気 象 庁 格子 の 全 球 解 析 値 を 川 い た 03,CO2, ア ロ ゾ ル な ど そ の 他 の 大 気 要 素 は,LOW- TRAN6v)中 緯 度 帯 冬 の モ デ ル 人 気 を 用 い た 全 球 解 析 値 は4(10mhよ な い の で,3.2.2頂 り上 空 の 水 蒸 気 量 に つ い て の 情 報 が で 述 べ た 方 法 で400mbよ 水 蒸 気 量 を推 定 し,次 に,対 り上 空 の 象 地 域0)中 心 の 代 表 温 度, 水 蒸 気 鉛.直 プ ロ フ ァ イ ル は 周 囲 の4点 の格子 での線型 内 挿 に よ る 方 法 で 求 め た 以上 の 方 法 で 求 め た 地域A, 33(211)

Table 7 Satellite Zenith Angles Observed in the Center of Researched Regions. Table 6 Same as Table 3 except at the Grid Point (19.5N, 137.OE) Table 8 The R.M.S.E. of the Estimated Values together with the Values of a, b, Correlation Coefficient between Observed R2 and R, and Threshhold Temperature of Channel 3 for Cirrus. Fig. 10 Radiance of the cirrus at A in Fig. 8 observed with Channel-2 (H20 absorption channel) vs that with Channel-3 (Window channel). Numerals are frequency.

Table 9 Same as Table 8 except in the Region (B) Table 10 Same as Table 8 except in the Region Table 11 Same as Table 8 except in the Region Fig. 11 The calculation of cirrus cloud height in the region (A) by the present model. Table 12 Results of Calculation of Cirrus Cloud Height by the Present Model and Szejwach's Method (1982).

Table 13 Mininum Effective Emissivity of Cirrus Cloud for Channel 3 Obtained from the Present Model. Fig. 15 Vertical profiles of air and dew-point temperatures from a routine rawinsonde observation at Vladivostok Aerological Observatory (43.1N, 131.9E).

1) Manabe, S. and R.F. Strikcker : Thermal equilibrium of the atmosphere with a convective adjustment. J. Atmos. Sci., 21, 361-385, 1964. 2) Cox, S.K. : Cirrus clouds and the climate. J. Atmos. Sci., 28, 1513-1515, 1971. 3) Park, S.U., D.N. Sikdar and V.E. Suomi : Correlation between thickness and brightness using Nimbus-4 THIR data and ATS-3 digital data. J. Appl. Meteor., 13, 402-410, 1973. 4) Shenk, W.E. and R.J. Currain : A multispectral method for estimation of cirrus cloud top heights. J. Appl. Meteor., 12, 1213-1216, 1973. 5) Szejwach, G.: Determination of semitransparent cirrus cloud temperature from infrared radiances : Application to METEOSAT. J. Appl. Meteor., 21, 384-393, 1982. 6) Inoue, T.:On the temperature and effective emissivity determination of semi-transparent cirrus clouds by bi-spectral measurements in the 10,um window region. J. Meteor. Soc. Japan, 63, 88-99, 1985. 7) Heymsfield, A.J. 1975 : Cirrus uncinus generating cells and evolutin of cirriform clouds. Part I. Aircraft measurements of the growth of the ice phase. J.Atmos. Sci., 32, 799-808. 8) Liou, K.N. 1974 : On the radiative properties of cirrus in the window region and their influence on remote sensing of the atmosphere. J. Atmos. Sci., 31, 522-532. 9) Irvine, W.M. and G.B. Pollack. 1968 : Infrared optical properties Icarus, 8, 324-360. of water and ice spheres.

ú { ƒšƒ [ ƒgƒz ƒ ƒvƒ ƒošw ïž Vol.10No.2 tance/radiance : Computer Code LOWTRAN- 6. AFGL-TR-83-0287 (Air Force Geophysics Laboratory. Hanscom AFB, MAO 1731), 1983. 12) Japan Meteorological Agency, Aerological data of Japan. Atmospheric ozone atmospheric electricity long wave radiation dew-point 13) Tsuji, M. "MOS-1 data CCT format up dates", 1 st MOS-1 management and operation group (MOMO) meeting, July, 1988. 14) Appleman, H.S.: Occurrence and forecasting of cirrostratus clouds. Technical Note NO. 40, WMO, 1968. temuerature (1969.1970),241-248.1472