Alfred C. Holland

ANALYTICAL AND EXPERIMENTAL INVESTIGATION OF LIGHT SCATTERING FROM POLYDISPERSIONS OF MIE PARTICLES.

A comparison has been made between (1) the computed angular scattering coefficient for a polydisperse cloud of small, spherical (Mie) particles and (2) the measured angular scattering coefficient for a polydisperse cloud of irregular, randomly oriented (Mie) particles fitting the same distribution function and having the same material properties. The comparison has been made for eight wavelengths covering the visible range.

Improved rocket ozonesonde (ROCOZ-A). 1: Demonstration of precision.

Measurements of the daytime ozone distribution in the stratosphere have been made with an improved rocket ozonesonde (ROCOZ-A). Vertical cumulative ozone as a function of geometric altitude is the basic information content of these measurements. The instrument-to-instrument repeatability of the ozonesonde was determined by two series of four soundings each. At one standard deviation the instrument repeatability averages from 2.0 to 2.5% over the entire altitude range of the instrument. The worst measured repeatability is 3.7% at 55 km for one of the flight series.

Ozone estimates derived from Dobson direct sun measurements: effect of atmospheric temperature variations and scattering

We have performed an analysis of the impact of the temperature sensitivity of the ozone absorption coefficients on estimates of total atmospheric ozone obtained by the Dobson spectrophotometer operating in direct sun mode. In general, the higher the mean ozone temperature the greater will be the tendency to overestimate the ozone amount. The spreads in ozone residuals over the temperature models we investigated were 3%, 4%, and 6% for the A, C, and D line pairs, respectively, whereas for coupled line pairs the spread was only about 2%. The A-C-D triplet showed a very small temperature effect, the spread being probably less than 2%. For the A-D system, currently recommended by the WMO, the computed spread was 2.4 +/- 0.5%. A Monte Carlo model was applied to investigate the potential impact of scattered radiation entering the system. The effect has been computed for various conical fields of view. For clear sky conditions with no aerosols present, the error introduced appears to be less than 1%. When a tropospheric aerosol model was inserted, however, significant errors were observed. For the models we studied aerosol attenuation resulted in overestimates of total ozone up to 8%, but the impact of scattered radiation was to reduce the overestimate, and, in some cases, the scattering and attenuation effects may balance for a realistic Dobson system. Both effects increased from the A to the C to the D line pairs. The results indicate that line pair coupling reduces the combined error due to both sources to less than 1%.

Information content of sky intensity and polarization measurements at right angles to the solar direction

This paper presents the results of a Monte Carlo simulation study of the brightness and polarization at right angles to the solar direction both for ground-based observations (looking up) and for satellite-based systems (looking down). Calculations have been made for a solar zenith angle whose cosine was 0.6 and wavelengths ranging from 3500 A to 9500 A. We have succeeded in demonstrating a sensitivity of signatures to total aerosol loading, aerosol particle size distribution and refractive index, and the surface reflectance albedo. For Lambertian type surface reflection the albedo effects enters solely through the intensity sensitivity, and we have found very high correlations between the polarization term signatures for the ground-based and satellite-based systems. Potential applications of these results for local albedo predictions and satellite imaging systems recalibrations are discussed.

Validation of the BUV satellite ozone sensor using the rocket ozonesonde.

This paper reviews aspects of the rocket ozonesonde (ROCOZ) performance pertaining to the validation of satellite ozone sensing systems, particularly the backscattered ultraviolet (BUV) sensor. It is shown that while the BUV system relates cumulative vertical ozone to pressure, the ROCOZ can measure cumulative ozone as a function of radar altitude. As a consequence some method of relating atmospheric pressure and altitude is required, with a concomitant error introduced. A Monte Carlo simulation was performed to evaluate the contribution of scattered flux on the ROCOZ result. The scattered component always causes an underestimate in cumulative ozone that increases almost linearly with pressure and is only weakly dependent on the solar zenith angle. For most practical operating conditions, however, the error in cumulative ozone arising from the scattered flux is of the order of 1% or less.