The development of a coherent laser radar system using 2- mu m Tm- and Tm, Ho-doped solid-state lasers, which is useful for the remote range-resolved measurement of atmospheric winds, aerosol backscatter, and differential absorption lidar (DIAL) measurements of atmospheric water vapor and CO/sub 2/ concentrations, is described. Measurements made with the 2- mu m coherent laser radar system, advances in the laser technology, and atmospheric propagation effects on 2- mu m coherent lidar performance are discussed. Results include horizontal atmospheric wind measurements to >20 km. vertical wind measurements to >5 km, near-horizontal cloud returns to 100 km, and hard target (mountainside) returns from 145 km. >

Coherent laser radar at 2μm using solid - state lasers

Coherent laser radar at 2 mu m using solid-state lasers

A detailed description of the goals and methodology of the First International Satellite Cloud Cover Project Regional Experiment (FIRE) is presented The purpose of the experiment is to develop physical models and parameterizations of fractional cloud cover over the Pacific Basin In order to determine fractional cloud cover parameters, satellite observations by radar and lidar instruments will be combined with in situ measurements of the cloud-capped marine boundary layer A description of a candidate experiment for the program is presented, and some general problems connected with the statistical characterization of satellite imagery are discussed

Outlook for research on subtropical marine stratiform clouds

The emissivity model for rough sea surface [Remote Sensing Environ.24, 313–329 (1988)] is inspected in
light of the measured surface emissivity. In the presence of moderate wind (5
m/s or less), the emissivity model is found to be adequate for small to
moderate view angles. For large view angles, the discrepancy between the
computed and the measured emissivity is large, but one can reduce this
considerably by incorporating the reflected sea surface emission into the
emissivity model. In addition, examination of the spectral variation of the
observed and computed emissivity suggests the need for refined measurements of
the complex refractive index. An improved model is constructed to calculate
the rough sea surface emissivity that can be used to provide accurate
estimates of sea surface skin temperatures from remotely sensed radiometric
measurements. An important feature of the improved model is that the computed
sea surface emissivity is only weakly dependent on wind speed for most view
angles used in practice.

Emissivity of rough sea surface for 8–13 µm: modeling and verification

The diffraction theory of optical scintillations has so far failed to describe the propagation of light over paths where the integrated amount of refractive-index turbulence is sufficient to cause saturation of the scintillations. We present a simple, physically based elaboration of the first-order perturbation theory and compare it with observations. Our theory reproduces in detail the observed saturation curve and the observed spatial covariance of the scintillations. In particular, we show why the fine-scale structure of scintillations persists deep into the saturation regime.

Saturation of optical scintillation by strong turbulence

Wind fields measured with a pulsed infrared (CO2) Doppler lidar are compared with measurements by in situ anemometers, balloons, and radar. Radial winds were measured at slant ranges between 1.5 and 12 km during the various comparisons. The standard deviation of the differences between the lidar and the other measurement methods varied from 0.34 m sec−1 for sonic anemometer comparisons to 2.5 m sec−1 for balloon methods. Differences may be due to an inherent difficulty in comparing spatial and temporal averages of winds.

Wind measurement accuracy of the NOAA pulsed infrared Doppler lidar.

A detailed computer simulation of the Windsat global wind measuring process has been developed and used to establish error limits as a function of design parameters. Studies were conducted for a Windsat research system in a 300- and an 800-km orbit. Wind measuring errors were <2 m sec−1 in the troposphere for the recommended set of parameters. Our study results indicate the feasibility of measuring global winds from a space platform using a coherent laser radar.

Feasibility studies for a global wind measuring satellite system (Windsat): analysis of simulated performance.

A systematic program of observing atmospheric backscatter β profiles from 4 to 16-km above sea level is described. Initial monthly averages indicating a lognormal distribution are presented. Cirrus prevalence, volcanic layers in the stratosphere, diurnal effects, convection, calibration, and absorption effects are discussed as well.

Aerosol backscattering profiles at λ = 10.6 μm

We determine the backscatter reflectance (more properly the bidirectional reflectance distribution function at a 45° angle of incidence and observation) for circularly polarized radiation of λ = 10.6 μm for 120-grit aluminum oxide sandcloth (1.5 × 10−2 sr−1) and 400-grit silicon carbide sandpaper (1.1 × 10−2 sr−1) with respect to sublimed flowers of sulfur (1.8 × 10−1 sr−1). The effect of range and the atmospheric effect of turbulence-induced beam wander are discussed for both rotating disks and linearly translated belts. The advantages of large slowly rotating disks for field calibrations are presented.

Freeman F. Hall

Papers

Wind measurement accuracy of the NOAA pulsed infrared Doppler lidar.

Feasibility studies for a global wind measuring satellite system (Windsat): analysis of simulated performance.

Aerosol backscattering profiles at λ = 10.6 μm

Calibration of coherent lidar targets

Visibility reductions from soil dust in the Western U.S.