THE EXTRACTION OF THE THERMAL EMISSION BAND OF METHANE FROM THE LONGWAVE SPECTRUM OF THE ATMOSPHERE

The thermal emission band at 1306 cm(-1) of atmospheric methane, an im portant greenhouse gas, is presented for a cold, clear day in January 1994. A spectrum of the nonmethane emission features has been simulate d using the FASCD3P radiation code and measured radiosonde profiles of temperature, pressure, and relative humidity. This has enabled a succ essful subtraction of interfering emission features from the methane e mission region. The methane radiance has been simulated using the FASC D3P radiation code. A comparison of the observed and simulated emissio n bands of methane shows good agreement at all frequencies of emission . From these measurements the total downward greenhouse radiative flux at the ground from the methane emission band for a cold, clear winter day has been determined to be 1.7 W m(-2) +/- 10%.