Using high-resolution Fourier-transform infrared absorbance and transmittance spectral data for ammonium sulfate (AMS), calcium carbonate (CAC), and ammonium nitrate (AMN), we made comparisons with previously published complex reactive-index data for AMS and CAC to infer experimental parameters to determine the imaginary refractive index for AMN in the infrared wavelength range from 2 to 20 microm. Subtractive Kramers-Kronig mathematical relations were applied to calculate the real refractive index for the three compositions. Excellent agreement for AMS and CAC with the published values was found, validating the complex refractive index obtained for AMN. We performed backscatter calculations using a log-normal size distribution for AMS, AMN, and CAC aerosols to show differences in their backscattered spectra.

Aerosol concentrations and size distributions in the middle and upper troposphere over the remote Pacific Ocean were measured with a forward scattering spectrometer probe (FSSP) on the NASA DC‐8 aircraft during NASA's Global Backscatter Experiment (GLOBE) in May–June 1990. The FSSP size channels were recalibrated based on refractive index estimates from flight‐level aerosol volatility measurements with a collocated laser optical particle counter (LOPC). The recalibrated FSSP size distributions were averaged over 100‐s intervals, fitted with lognormal distributions and used to calculate aerosol backscatter coefficients at selected wavelengths. The FSSP‐derived backscatter estimates were averaged over 300‐s intervals to reduce large random fluctuations. The smoothed FSSP aerosol backscatter coefficients were then compared with LOPC‐derived backscatter values and with backscatter measured at or near flight level from four lidar systems operating at 0.53, 1.06, 9.11, 9.25, and 10.59 μm. Agreement between FSSP‐derived and lidar‐measured backscatter was generally best at flight level in homogeneous aerosol fields and at high backscatter values. FSSP data often underestimated low backscatter values especially at the longer wavelengths due to poor counting statistics for larger particles (>0.8 μm diameter) that usually dominate aerosol backscatter at these wavelengths. FSSP data also underestimated backscatter at shorter wavelengths when particles smaller than the FSSP lower cutoff diameter (0.35 μm) made significant contributions to the total backscatter.

Reliable climate forecasting using numerical models of the ocean‐atmosphere system requires accurate data sets of sea surface temperature (SST) and surface wind stress. Global sets of these data will be supplied by the instruments to fly on the ERS 1 satellite in 1990. One of these instruments, the Along‐Track Scanning Radiometer (ATSR), has been specifically designed to provide SST in cloud‐free areas with an accuracy of 0.3 K. The expected capabilities of the ATSR can be assessed using transmission models of infrared radiative transfer through the atmosphere. The performances of several different models are compared by estimating the infrared brightness temperatures measured by the NOAA 9 AVHRR for three standard atmospheres. Of these, a computationally quick spectral band model is used to derive typical AVHRR and ATSR SST algorithms in the form of linear equations. These algorithms show that a low‐noise 3.7‐μm channel is required to give the best satellite‐derived SST and that the design accuracy of the ATSR is likely to be achievable. The inclusion of extra water vapor information in the analysis did not improve the accuracy of multiwavelength SST algorithms, but some improvement was noted with the multiangle technique. Further modeling is required with atmospheric data that include both aerosol variations and abnormal vertical profiles of water vapor and temperature.

An aerosol microphysics dataset was used to model backscatter in the 0.35-11-mum wavelength range, with the results validated by comparison with measured cw and pulsed lidar backscatter obtained during two NASA-sponsored airborne field experiments. Different atmospheric features were encountered, with aerosol backscatter ranging over 4 orders of magnitude. Modeled conversion functions were used to convert existing lidar backscatter datasets to 2.1 mum. Resulting statistical distribution shows the midtropospheric aerosol backscatter background mode of beta(2.1) to be between ~3.0 x 10(-10) and ~1.3 x 10(-9) m(-1) sr(-1), ~10-20 times higher than that for beta(9.1); and a beta(2.1) boundary layer mode of ~1.0 x 10(-7) to ~1.3 x 10(-6) m(-1) sr(-1), ~3-5 times higher than beta(9.1).

On the basis of a modified version of the LOWTRAN 6 model, an absolute comparison is made of typical and background-limited IR sensors operating in the 3-5-microm and 8-12-microm wavebands in a tropical maritime environment. Allowance is made for slant paths and a variety of targets and backgrounds including hot targets and backgrounds spectrally different from the targets. It is found that with current detector technology the 8-12-microm waveband is superior for all except very hot targets at long ranges. The validity of various approximations is also investigated, and in particular it is found that the blackbody composite background approximation should not be used for slant paths.