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A. J. Drummond

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A. J. DRUMMOND

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A. J. Drummond
and
J. J. Roche

Abstract

This paper demonstrates, in summary form, some corrections to be made to values of spectral flux as measured with Eppley spectral pyranometers. The results of an investigation into the occurrence of what are believed to be systematic errors in scaled hemispherical thermopile systems, employed in pyranometer design, are presented. This investigation was prompted by an analysis of a large mass of solar spectral measurement material, which indicated an apparent change in spectral pyranometer sensitivity under conditions of continuous operation. The study also included pyranometers of natural- and forced-ventilated design.

The results indicate that the corrections so far established ought to be of general application, within practical limits, to the present Eppley spectral pyranometer and, perhaps with some modifications, to other constructions.

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A. K. Ångström
and
A. J. Drummond

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In radiation meteorology, accurate filter measurements are of importance, particularly for the determination of the parameters of atmospheric transmission. This paper attempts to review the more important aspects involved in such filter measurements and includes a summary of the authors' previous investigations concerned with the establishment of the constants for the standard-type filters recommended by the World Meteorological Organization.

Tables are given to facilitate correcting solar-radiation measurements made with filter specimens exhibiting different characteristics within the same glass type to standard conditions. Also presented are tabular values indicating the genera1 effect on measurements (made with the series of Schott OG1, RG2 and RG8 filters examined here) introduced by variation of 10 μ in the lower cutoff position (a shift which has frequently occurred in samples of the same glass type from different melts) ; the information relates to solar radiation at specified air mass and turbidity.

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A. J. Drummond
and
A. R. Karoli
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J. R. Drummond
and
A. Ashton

Abstract

The pressure modulator is extensively used in atmospheric measurements but is not well characterized in terms of its spectroscopic operation. A series of measurements on a carbon monoxide radiometer is described and comparisons are made with theoretical calculations for the same conditions. Agreement is found between theory and experiment for normalized cell transmissions. Diode laser spectroscopic measurements are also found to give satisfactory agreement if there is some temperature cycling in the modulator cell. Some variation is found in the absolute measurements of equivalent width. The possible reasons for this discrepancy are discussed.

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A. J. Drummond
and
E. Vowinckel

Abstract

Since about 1950, considerable emphasis has been placed upon the registration of solar radiation in Africa by a number of the meteorological services of the territories on the continent. It is now considered that sufficient data have been assembled, with the earlier series of measurements available, to permit undertaking of the first cartographical presentation of the total short-wave radiation incomes over southern Africa. Unfortunately there is, at present, insufficient material to allow the maps to be extended northward of the equator. Twenty-three series have been used in the construction of summer and winter seasonal maps; computed values at seven other locations were employed to improve the presentation.

The seasonal areal distributions of the solar radiation, on a horizontal surface, are compared with those for the continental United States for the corresponding summer and winter periods.

At ten of the stations forwarding data regularly to the World Meteorological Organization radiation center at Pretoria, records of the diffuse sky component are separately available. With the derived, average indirect fluxes for Brukkaros — the old Smithsonian Institution station in South-West Africa — these measurements constitute the densest network of its kind anywhere. The general results are discussed.

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A. M. Drummond
and
J. I. MacPherson

Abstract

A theoretical model for the local flow velocity ahead of the wing quarter-chord point on the National Aeronautical Establishment Twin Otter has been developed and experimentally verified by flight measurements using a pitot-static equipped Particle Measuring Systems (PMS) canister. This flow velocity model was used to calculate drop trajectories and the resulting airflow effects on drop images and concentrations. Results indicate that drop images and concentrations measured by the Twin Otter are distorted in the worst case by no more than 25% for an unusually high aircraft lift coefficient (CL ) of 0.79, and by only a few percent for lower values of CL typical of normal flight. A method to correct water drop images and concentrations is described and results for a PMS probe mounted at one underwing station are presented.

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A. J. Drummond
and
Sigmund Fritz
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J. R. Drummond
,
D. Turner
, and
A. Ashton

Abstract

The determination of the horizontal attitude of a balloon-borne, infrared, limb-scanning radiometer is discussed. In particular, the relationship between scan-angle, as measured by the instrument, and the tangent height of the ray path through the atmosphere is considered. The instrument is unusual in that it scans in two opposite directions. This property is used to derive the scan angle from the same radiance profiles, which are used to determine the constituent profiles, subject only to the assumptions that the attitude is steady, the stratosphere is locally horizontally homogeneous, and the instrumental optical alignment is correct.

The results of this determination for the first flight of the Toronto Balloon Radiometer are compared to previous methods of determining the instrumental scan angle and are found to agree to the accuracy with which the comparisons are made. Techniques by which the accuracy and resolution of the two-sided attitude determination could be improved are discussed.

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