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  • Author or Editor: Robert H. Johns x
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Thomas B. Sanford, Robert G. Driver, and John H. Dunlap

Abstract

A freely failing current meter called the Absolute Velocity Profiler (AVP) is described. This profiler is an expansion of a previously developed instrument, the Electro-Magnetic Velocity Profiler (EMVP), with the additional capability of acoustic Doppler (AD) measurements to determine the reference velocity for the EM profiles. The AVP measures the motional electric currents in the sea and the Doppler frequency shin of bottom-scattered echoes. The EM measurements yield a profile of the horizontal components of velocity relative to a depth-independent reference velocity; the AD measurements determine the absolute velocity of the AVP with respect to the seafloor. The EM profile is obtained from the sea surface to the bottom, and the AD measurements are obtained within about 60–300 m of the seafloor. The combination of the EM and AD measurements yields an absolute velocity profile throughout the water column. Performance analyses show the method is accurate to within 1–2 cm s−1 rms. The profiler also measures temperature and its gradient.

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H. Lee Kyle, Richard Hucek, Philip Ardanuy, Lanning Penn, Brian Groveman, John Hickey, and Robert Maschoff

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This paper describes the production calibration adjustment algorithms used to remove thermal perturbation and stray light noise signals from the Nimbus-7 earth radiation budget (ERB) measurements. Sunlight, both direct and scattered from the sensor baffles, contaminated the ERB measurements at satellite sunrise and sunset. The problem covered subsatellite solar zenith angles from 90° to 120° and reduced the usefulness of the longwave spectral radiation measurements. Scattered light corrections are made from 90° to 99° while orbit-by-orbit interpolation is used frown 99° to 121°. Tests indicate that in the mean the midpoint interpolation error is less than 1 W m−2 with a standard deviation of about 5 W m−2. Thermal perturbations on the total channel 12 (0.2–50 μm) appeared to be always less than 0.3%. However, the Suprasil-W domes on the otherwise similar shortwave channels 13 and 14 in some way helped produce thermal perturbations of up to 6% or more in channel 13 (0.2–3.8 μm and up to 3% or more in channel 14 (0.7–2.8 μm). These perturbations arose from variations in external radiant heating during the day, night, sunrise, and sunset. In addition, the on/off cycles of the ERB and neighboring experiments produced day-to-day variations. The algorithms described here helped produce a stable 9-year-long measurement set. No thermal corrections were made in channel 12 and the obvious thermal perturbations in channels 13 and 14 were corrected. The absolute accuracy of the calibrated measurements is difficult to determine. The remaining uncertainty depends on the perturbing functions that were greater at high latitudes, near satellite sunrise and sunset, than in the Tropics. In June and July, the corrections for the daytime thermal perturbations near the North Pole may be too large by 3–5 W m−2. In general, the Nimbus-7 ERB products show good agreement with the follow-on Earth Radiation Budget Experiment (ERBE) products.

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Lynn M. Russell, Shou-Hua Zhang, Richard C. Flagan, John H. Seinfeld, Mark R. Stolzenburg, and Robert Caldow

Abstract

A radially classified aerosol detector (RCAD) for fast characterization of fine particle size distributions aboard aircraft has been designed and implemented. The measurement system includes a radial differential mobility analyzer and a high-flow, high-efficiency condensation nuclei counter based on modifications to a commercial model (TST, model 3010). Variations in pressure encountered during changes in altitude in flight are compensated by feedback control of volumetric flow rates with a damped proportional control algorithm. Sampling resolution is optimized with the use of an automated dual-bag sampling system. This new system has been tested aboard the University of Washington Cl31a research aircraft to demonstrate its in-flight performance capabilities. The system was used to make measurements of aerosol, providing observations of the spatial variability within the cloud-topped boundary layer off the coast of Monterey, California.

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Robert B. Lee III, Bruce R. Barkstrom, G. Louis Smith, John E. Cooper, Leonard P. Kopia, R. Wes Lawrence, Susan Thomas, Dhirendra K. Pandey, and Dominique A. H. Crommelynck

Abstract

The Clouds and the Earth's Radiant Energy System (CERES) spacecraft sensors are designed to measure broadband earth-reflected solar shortwave (0.3–5 µm) and earth-emitted longwave (5– > 100 µm) radiances at the top of the atmosphere as part of the Mission to Planet Earth program. The scanning thermistor bolometer sensors respond to radiances in the broadband shortwave (0.3–5 µm) and total-wave (0.3– > 100 µm) spectral regions, as well as to radiances in the narrowband water vapor window (8–12 µm) region. The sensors are designed to operate for a minimum of 5 years aboard the NASA Tropical Rainfall Measuring Mission and Earth Observing System AM-I spacecraft platforms that are scheduled for launches in 1997 and 1998, respectively. The flight sensors and the in-flight calibration systems will he calibrated in a vacuum ground facility using reference radiance sources, tied to the international temperature scale of 1990. The calibrations will be used to derive sensor gains, offsets, spectral responses, and point spread functions within and outside of the field of view. The shortwave, total-wave, and window ground calibration accuracy requirements (1 sigma) are ±0.8, ±0.6, and ±0.3 W m−2 sr−1, respectively, while the corresponding measurement precisions are ±0.5% and ±1.0% for the broadband longwave and shortwave radiances, respectively. The CERES sensors, in-flight calibration systems, and ground calibration instrumentation are described along with outlines of the preflight and in-flight calibration approaches.

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