*======================================================= * ROSENKRANZ (1998) model -- reference "Water vapor microwave * continuum absorption: a comparison of measurements and results" * To appear in Radio Science * * Top level interface (GasabsR98) by G. Petty * * This subroutine calculates the mass extinction coefficient of the * dry and vapor components of air. * * Input: * F = frequency (GHz), * Tk = absolute temperature (K) * Rhowv = water vapor density (kg/m**3). * Pa = Total air pressure (Pascals). * Output: * Absair = extinction by dry air (meters squared per kg *moist air*) * Abswv = extinction by water vapor (meters squared per kg water vapor) * * 2/8/2001 - fixed division by zero when rhowv = 0 (G. Petty) * SUBROUTINE GasabsR98(F,Tk,Rhowv,Pa,absair,abswv) * check for "reasonable" input values if (F .le. 0.0 .or. F .gt. 800.0) & stop 'Frequency out of range in GasabsR98' if (Tk .lt. 100.0) & stop 'Temperature out of range in GasabsR98' if (pa .lt. 10.0 .or. pa .gt. 1.2e5) & stop 'Pressure out of range in GasabsR98' * convert pressure from Pa to Mb pmb = pa/100.0 * convert vapor density from kg/m**3 to g/m**3 vapden = rhowv*1000.0 * get volume extinction coefficients absair = absn2(tk,pmb,f) + o2abs(tk,pmb,vapden,f) abswv = abh2o(tk,pmb,vapden,f) * * convert vapor density to vapor pressure e = rhowv*(tk*461.5) * calculate specific humidity q = 0.622*e/pa * calculate virtual temperature tv = (1. + 0.61*q)*tk * moist air density rhoair = pa/(tv*287.06) * convert above from Np/km to m**2/kg absair = 0.001*absair/rhoair if (rhowv .eq. 0.0) then abswv = 0.0 else abswv = 0.001*abswv/rhowv endif return end ******************************************************************* *This file contains subroutines for computing atmospheric absorption at *microwave wavelengths, as supplied by P. Rosenkranz (2/98) via his *anonymous ftp server (mesa.mit.edu; login anonymous; go to phil/lpl_rt)AN *Consolidated into one file by G. Petty * *********************************************************** * Begin summaries *********************************************************** * FUNCTION ABSN2(T,P,F) C ABSN2 = ABSORPTION COEFFICIENT DUE TO NITROGEN IN AIR C (NEPER/KM) C T = TEMPERATURE (K) C P = PRESSURE (MB) C F = FREQUENCY (GHZ) C ************************************************************************* * FUNCTION O2ABS(TEMP,PRES,VAPDEN,FREQ) C C PURPOSE: RETURNS ABSORPTION COEFFICIENT DUE TO OXYGEN IN AIR, C IN NEPERS/KM C C NAME UNITS DESCRIPTION VALID RANGE C C TEMP KELVIN TEMPERATURE (UNCERTAIN) C PRES MILLIBARS PRESSURE (3 TO 1000) C VAPDEN G/M**3 WATER VAPOR DENSITY (ENTERS LINEWIDTH CALCULATION C DUE TO GREATER BROADENING EFFICIENCY OF H2O) C FREQ GHZ FREQUENCY (0 TO 900) ************************************************************** * FUNCTION ABH2O(T,P,RHO,F) C C PURPOSE- COMPUTE ABSORPTION COEF IN ATMOSPHERE DUE TO WATER VAPOR C C NAME UNITS I/O DESCRIPTON VALID RANGE C T KELVIN I TEMPERATURE C P MILLIBAR I PRESSURE .1 TO 1000 C RHO G/M**3 I WATER VAPOR DENSITY C F GHZ I FREQUENCY 0 TO 800 C ABH2O NEPERS/KM O ABSORPTION COEFFICIENT C ***************************************************************** * FUNCTION ABLIQ(WATER,FREQ,TEMP) C COMPUTES ABSORPTION IN NEPERS/KM BY SUSPENDED WATER DROPLETS C FROM EQUATIONS OF LIEBE, HUFFORD AND MANABE C (INT. J. IR & MM WAVES V.12(17) JULY 1991 C WATER IN G/M**3 C FREQ IN GHZ (VALID FROM 0 TO 1000 GHZ) C TEMP IN KELVIN C PWR 8/3/92 C ************************************************************** * * Begin actual function definitions * *************************************************************** FUNCTION ABSN2(T,P,F) C ABSN2 = ABSORPTION COEFFICIENT DUE TO NITROGEN IN AIR C (NEPER/KM) C T = TEMPERATURE (K) C P = PRESSURE (MB) C F = FREQUENCY (GHZ) C TH = 300./T ABSN2 = 6.4E-14*P*P*F*F*TH**3.55 RETURN END * * FUNCTION O2ABS(TEMP,PRES,VAPDEN,FREQ) C C PURPOSE: RETURNS ABSORPTION COEFFICIENT DUE TO OXYGEN IN AIR, C IN NEPERS/KM C C 5/1/95 P. Rosenkranz C C ARGUMENTS: REAL TEMP,PRES,VAPDEN,FREQ C C NAME UNITS DESCRIPTION VALID RANGE C C TEMP KELVIN TEMPERATURE (UNCERTAIN) C PRES MILLIBARS PRESSURE (3 TO 1000) C VAPDEN G/M**3 WATER VAPOR DENSITY (ENTERS LINEWIDTH CALCULATION C DUE TO GREATER BROADENING EFFICIENCY OF H2O) C FREQ GHZ FREQUENCY (0 TO 900) C C REFERENCE FOR EQUATIONS AND COEFFICIENTS: C P.W. ROSENKRANZ, CHAP. 2 AND APPENDIX, IN ATMOSPHERIC REMOTE SENSING C BY MICROWAVE RADIOMETRY (M.A. JANSSEN, ED. 1993) C AND H.J. LIEBE ET AL, JQSRT V.48, PP.629-643 (1992) C (EXCEPT: SUBMILLIMETER LINE INTENSITIES FROM HITRAN92) C COMMON /O2COM/ X,WB300,W300(40),F(40),Y300(40),S300(40), & V(40),BE(40) C LINES ARE ARRANGED 1-,1+,3-,3+,ETC. IN SPIN-ROTATION SPECTRUM DATA F/118.7503, 56.2648, 62.4863, 58.4466, 60.3061, 59.5910, 2 59.1642, 60.4348, 58.3239, 61.1506, 57.6125, 61.8002, 3 56.9682, 62.4112, 56.3634, 62.9980, 55.7838, 63.5685, 4 55.2214, 64.1278, 54.6712, 64.6789, 54.1300, 65.2241, 5 53.5957, 65.7648, 53.0669, 66.3021, 52.5424, 66.8368, 6 52.0214, 67.3696, 51.5034, 67.9009, 368.4984, 424.7631, 7 487.2494, 715.3932, 773.8397, 834.1453/ DATA S300/.2936E-14,.8079E-15, .2480E-14,.2228E-14, & .3351E-14,.3292E-14, .3721E-14,.3891E-14, & .3640E-14,.4005E-14, .3227E-14,.3715E-14, & .2627E-14,.3156E-14, .1982E-14,.2477E-14, & .1391E-14,.1808E-14, .9124E-15,.1230E-14, & .5603E-15,.7842E-15, .3228E-15,.4689E-15, & .1748E-15,.2632E-15, .8898E-16,.1389E-15, & .4264E-16,.6899E-16, .1924E-16,.3229E-16, & .8191E-17,.1423E-16, .6460E-15, .7047E-14, .3011E-14, & .1826E-14, .1152E-13, .3971E-14/ DATA BE/.009,.015, .083,.084, 2*.212, 2*.391, 2*.626, & 2*.915, 2*1.260, 1.660,1.665, 2.119,2.115, 2.624,2.625, & 2*3.194, 2*3.814, 2*4.484, 2*5.224, 2*6.004, 2*6.844, & 2*7.744, .048, .044, .049, .145, .141, .145/ C WIDTHS IN MHZ/MB DATA WB300/.56/, X/.8/ DATA W300/1.63, 1.646, 1.468, 1.449, 1.382, 1.360, & 1.319, 1.297, 1.266, 1.248, 1.221, 1.207, 1.181, 1.171, & 1.144, 1.139, 1.110, 1.108, 1.079, 1.078, 2*1.05, & 2*1.02,2*1.00,2*.97,2*.94,2*.92,2*.89, 3*1.92, 3*1.81/ DATA Y300/ -0.0233, 0.2408, -0.3486, 0.5227, & -0.5430, 0.5877, -0.3970, 0.3237, -0.1348, 0.0311, & 0.0725, -0.1663, 0.2832, -0.3629, 0.3970, -0.4599, & 0.4695, -0.5199, 0.5187, -0.5597, 0.5903, -0.6246, & 0.6656, -0.6942, 0.7086, -0.7325, 0.7348, -0.7546, & 0.7702, -0.7864, 0.8083, -0.8210, 0.8439, -0.8529, 6*0./ DATA V/ 0.0079, -0.0978, 0.0844, -0.1273, & 0.0699, -0.0776, 0.2309, -0.2825, 0.0436, -0.0584, & 0.6056, -0.6619, 0.6451, -0.6759, 0.6547, -0.6675, & 0.6135, -0.6139, 0.2952, -0.2895, 0.2654, -0.2590, & 0.3750, -0.3680, 0.5085, -0.5002, 0.6206, -0.6091, & 0.6526, -0.6393, 0.6640, -0.6475, 0.6729, -0.6545, 6*0./ C TH = 300./TEMP TH1 = TH-1. B = TH**X PRESWV = VAPDEN*TEMP/217. PRESDA = PRES -PRESWV DEN = .001*(PRESDA*B + 1.1*PRESWV*TH) DFNR = WB300*DEN SUM = 1.6E-17*FREQ*FREQ*DFNR/(TH*(FREQ*FREQ + DFNR*DFNR)) DO 32 K=1,40 DF = W300(K)*DEN Y = .001*PRES*B*(Y300(K)+V(K)*TH1) STR = S300(K)*EXP(-BE(K)*TH1) SF1 = (DF + (FREQ-F(K))*Y)/((FREQ-F(K))**2 + DF*DF) SF2 = (DF - (FREQ+F(K))*Y)/((FREQ+F(K))**2 + DF*DF) 32 SUM = SUM + STR*(SF1+SF2)*(FREQ/F(K))**2 O2ABS = .5034E12*SUM*PRESDA*TH**3/3.14159 RETURN END ************************************************************** FUNCTION ABH2O(T,P,RHO,F) C C NAME- ABH2O LANGUAGE- FORTRAN 77 C C PURPOSE- COMPUTE ABSORPTION COEF IN ATMOSPHERE DUE TO WATER VAPOR C IMPLICIT NONE C CALLING SEQUENCE PARAMETERS- C SPECIFICATIONS REAL T,P,RHO,F,ABH2O C NAME UNITS I/O DESCRIPTON VALID RANGE C T KELVIN I TEMPERATURE C P MILLIBAR I PRESSURE .1 TO 1000 C RHO G/M**3 I WATER VAPOR DENSITY C F GHZ I FREQUENCY 0 TO 800 C ABH2O NEPERS/KM O ABSORPTION COEFFICIENT C C REFERENCES- C LINE INTENSITIES FROM HITRAN92 (SELECTION THRESHOLD= C HALF OF CONTINUUM ABSORPTION AT 1000 MB). C WIDTHS MEASURED AT 22,183,380 GHZ, OTHERS CALCULATED: C H.J.LIEBE AND T.A.DILLON, J.CHEM.PHYS. V.50, PP.727-732 (1969) & C H.J.LIEBE ET AL., JQSRT V.9, PP. 31-47 (1969) (22GHz); C A.BAUER ET AL., JQSRT V.37, PP.531-539 (1987) & C ASA WORKSHOP (SEPT. 1989) (380GHz); C AND A.BAUER ET AL., JQSRT V.41, PP.49-54 (1989) (OTHER LINES). C AIR-BROADENED CONTINUUM BASED ON LIEBE & LAYTON, NTIA C REPORT 87-224 (1987); SELF-BROADENED CONTINUUM BASED ON C LIEBE ET AL, AGARD CONF. PROC. 542 (MAY 1993), C BUT READJUSTED FOR LINE SHAPE OF C CLOUGH et al, ATMOS. RESEARCH V.23, PP.229-241 (1989). C C REVISION HISTORY- C DATE- OCT.6, 1988 P.W.ROSENKRANZ - EQS AS PUBL. IN 1993. C OCT.4, 1995 PWR- USE CLOUGH'S DEFINITION OF LOCAL LINE C CONTRIBUTION, HITRAN INTENSITIES, ADD 7 LINES. C OCT. 24, 95 PWR -ADD 1 LINE. C JULY 7, 97 PWR -SEPARATE COEFF. FOR SELF-BROADENING, C REVISED CONTINUUM. C C LOCAL VARIABLES: INTEGER NLINES,I,J PARAMETER (NLINES=15) REAL DF(2),S1(NLINES),B2(NLINES),W3(NLINES),FL(NLINES),X(NLINES), & WS(NLINES),XS(NLINES) REAL PVAP,PDA,DEN,TI,TI2,SUM,WIDTH,WSQ,S,BASE,RES,CON C LINE FREQUENCIES: DATA FL/22.2351, 183.3101, 321.2256, 325.1529, 380.1974, 439.1508, & 443.0183, 448.0011, 470.8890, 474.6891, 488.4911, 556.9360, & 620.7008, 752.0332, 916.1712/ C LINE INTENSITIES AT 300K: DATA S1/ .1310E-13, .2273E-11, .8036E-13, .2694E-11, .2438E-10, & .2179E-11, .4624E-12, .2562E-10, .8369E-12, .3263E-11, .6659E-12, & .1531E-08, .1707E-10, .1011E-08, .4227E-10/ C T COEFF. OF INTENSITIES: DATA B2/ 2.144, .668, 6.179, 1.541, 1.048, 3.595, 5.048, 1.405, & 3.597, 2.379, 2.852, .159, 2.391, .396, 1.441/ C AIR-BROADENED WIDTH PARAMETERS AT 300K: DATA W3/.00281, .00281, .0023, .00278, .00287, .0021, .00186, & .00263, .00215, .00236, .0026, .00321, .00244, .00306, .00267/ C T-EXPONENT OF AIR-BROADENING: DATA X/.69, .64, .67, .68, .54, .63, .60, .66, .66, .65, .69, .69, & .71, .68, .70/ C SELF-BROADENED WIDTH PARAMETERS AT 300K: DATA WS/.01349, .01491, .0108, .0135, .01541, .0090, .00788, & .01275, .00983, .01095, .01313, .01320, .01140, .01253, .01275/ C T-EXPONENT OF SELF-BROADENING: DATA XS/ .61, .85, .54, .74, .89, .52, .50, .67, .65, .64, .72, & 1.0, .68, .84, .78/ C IF(RHO.LE.0.) THEN ABH2O = 0. RETURN ENDIF PVAP = RHO*T/217. PDA = P -PVAP DEN = 3.335E16*RHO TI = 300./T TI2 = TI**2.5 C C CONTINUUM TERMS CON = (5.43E-10*PDA*TI**3 + 1.8E-8*PVAP*TI**7.5)*PVAP*F*F C C ADD RESONANCES SUM = 0. DO 30 I=1,NLINES WIDTH = W3(I)*PDA*TI**X(I) + WS(I)*PVAP*TI**XS(I) WSQ = WIDTH*WIDTH S = S1(I)*TI2*EXP(B2(I)*(1.-TI)) DF(1) = F - FL(I) DF(2) = F + FL(I) C USE CLOUGH'S DEFINITION OF LOCAL LINE CONTRIBUTION BASE = WIDTH/(562500. + WSQ) C DO FOR POSITIVE AND NEGATIVE RESONANCES RES = 0. DO 20 J=1,2 IF(ABS(DF(J)).LT.750.) RES = RES + WIDTH/(DF(J)**2+WSQ) - BASE 20 CONTINUE 30 SUM = SUM + S*RES*(F/FL(I))**2 ABH2O = .3183E-4*DEN*SUM + CON RETURN END ************************************************************** FUNCTION ABLIQ(WATER,FREQ,TEMP) C COMPUTES ABSORPTION IN NEPERS/KM BY SUSPENDED WATER DROPLETS C FROM EQUATIONS OF LIEBE, HUFFORD AND MANABE C (INT. J. IR & MM WAVES V.12(17) JULY 1991 C WATER IN G/M**3 C FREQ IN GHZ (VALID FROM 0 TO 1000 GHZ) C TEMP IN KELVIN C PWR 8/3/92 C COMPLEX EPS,RE IF(WATER.LE.0.) THEN ABLIQ = 0. RETURN ENDIF THETA1 = 1.-300./TEMP EPS0 = 77.66 - 103.3*THETA1 EPS1 = .0671*EPS0 EPS2 = 3.52 + 7.52*THETA1 FP = (316.*THETA1 + 146.4)*THETA1 +20.20 FS = 39.8*FP EPS = (EPS0-EPS1)/CMPLX(1.,FREQ/FP) + & (EPS1-EPS2)/CMPLX(1.,FREQ/FS) +EPS2 RE = (EPS-1.)/(EPS+2.) ABLIQ = -.06286*AIMAG(RE)*FREQ*WATER RETURN END FUNCTION VAPOR(T) C C COMPUTES SATURATION H2O VAPOR PRESSURE (OVER LIQUID) C USING LIEBE'S APPROXIMATION (CORRECTED) C C T IN KELVIN C VAPOR IN MBAR C PWR 4/8/92 C TH = 300./T VAPOR = 35.3*EXP(22.64*(1.-TH))*TH**5 RETURN END