Ship-Based Sun Photometer Measurements Using Microtops Sun Photometers

John N. Porter School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii

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Mark Miller Department of Applied Science, Brookhaven National Laboratory, Upton, New York

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Christophe Pietras SAIC-General Sciences Corporation, NASA Goddard Space Flight Center, Greenbelt, Maryland

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Craig Motell School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii

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Abstract

The use of hand-held Microtops II sun photometers (built by Solar Light Inc.) on ship platforms is discussed. Their calibration, filter stability, and temperature effects are also described. It is found that under rough conditions, the ship motion causes the largest error, which can result in a bias toward higher optical depths. In order to minimize this bias, a large number of sun photometer measurements (∼25) should be taken in a short period of time, and the higher values should be discarded. Under rough ocean conditions, it is also best to shorten the Microtops sun photometer sampling period (less than 5 s) and save only a single value (no averaging) and remove the high optical depths in postprocessing. It is found that the Microtops should be turned off frequently to correct for zero drift caused by temperature effects. Calibration is maintained by routine Langley plot calibrations at the Mauna Loa Observatory for each unit or through cross calibration.

Corresponding author address: John Porter, School of Ocean, Earth Science and Technology, University of Hawaii, 2525 Correa Road, Honolulu, HI 96822.

Email: jporter@soest.hawii.edu

Abstract

The use of hand-held Microtops II sun photometers (built by Solar Light Inc.) on ship platforms is discussed. Their calibration, filter stability, and temperature effects are also described. It is found that under rough conditions, the ship motion causes the largest error, which can result in a bias toward higher optical depths. In order to minimize this bias, a large number of sun photometer measurements (∼25) should be taken in a short period of time, and the higher values should be discarded. Under rough ocean conditions, it is also best to shorten the Microtops sun photometer sampling period (less than 5 s) and save only a single value (no averaging) and remove the high optical depths in postprocessing. It is found that the Microtops should be turned off frequently to correct for zero drift caused by temperature effects. Calibration is maintained by routine Langley plot calibrations at the Mauna Loa Observatory for each unit or through cross calibration.

Corresponding author address: John Porter, School of Ocean, Earth Science and Technology, University of Hawaii, 2525 Correa Road, Honolulu, HI 96822.

Email: jporter@soest.hawii.edu

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