Improved Accuracy in Shipborne Broadband Irradiance Measurements during
MARCUS using New Tilt-Corrected SHIPRAD Systems
Abstract
Surface broadband shortwave and longwave irradiance are key components
of the surface energy budget and give insight on atmospheric
constituents like clouds and aerosols as well as provide useful
information for model evaluation. Surface irradiance measurements are
particularly difficult to make over the ocean where few measurement
platforms exist, and where the motion of ships and buoys makes the
accuracy of the measurements challenging. During the US DOE ARM
Measurements of Aerosols, Radiation, and Clouds over the Southern Ocean
(MARCUS) field campaign, new shipborne broadband radiation systems
(SHIPRAD) were deployed for the first time to test correction. The
systems include pyrgeometer measurements for measuring longwave
irradiance, an unshaded pyranometer to measure shortwave irradiance, a
navigation system measuring pitch/roll/heading, and an SPN1 shortwave
radiometer that measures direct and diffuse components with no moving
parts. A tilt correction methodology was used to correct 1 second
temporal resolution shortwave irradiance data for ship motion, designed
to correct tilts of 10 degrees or less to within 10 W/m2. Two SHIPRAD
systems were deployed on the port and starboard sides of the ship, and
the measurements were combined in order to be able to eliminate
measurements shaded by ship structures. The new methodology allows for
high-temporal resolution irradiance measurements with higher accuracy.
Results will be presented on the accuracy of the tilt correction
methodology and the irradiance measurement results throughout the
campaign.