Analysis of shipboard aerosol optical thickness measurements from multiple sunphotometers aboard the R/V Ronald H. Brown during the Aerosol Characterization Experiment--Asia

Marine sunphotometer measurements collected aboard the R/V Ronald H. Brown during the Aerosol Characterization Experiment-Asia (ACE-Asia) are used to evaluate the ability of complementary instrumentation to obtain the best possible estimates of aerosol optical thickness and Angstrom exponent from ships at sea. A wide range of aerosol conditions, including clean maritime conditions and highly polluted coastal environments, were encountered during the ACE-Asia cruise. The results of this study suggest that shipboard hand-held sunphotometers and fast-rotating shadow-band radiometers (FRSRs) yield similar measurements and uncertainties if proper measurement protocols are used and if the instruments are properly calibrated. The automated FRSR has significantly better temporal resolution (2 min) than the hand-held sunphotometers when standard measurement protocols are used, so it more faithfully represents the variability of the local aerosol structure in polluted regions. Conversely, results suggest that the hand-held sunphotometers may perform better in clean, maritime air masses for unknown reasons. Results also show that the statistical distribution of the Angstrom exponent measurements is different when the distributions from hand-held sunphotometers are compared with those from the FRSR and that the differences may arise from a combination of factors.     

SPT Hammer Energy Ratio versus Drop Height

Automatic trip hammers have advantages for standard penetration test (SPT) of consistent drop height and low friction loss during hammer fall. These advantages, however, generate high energy transfer ratios (ER), typically about 90%. This efficiency causes lower sensitivity and higher energy correction coefficients, CE. To reduce ER and CE and to increase the sensitivity of SPT conducted at the Wildlife Liquefaction Array (WLA) and the Garner Valley Downhole Array, instrumented Network for Earthquake Engineering Simulation sites, a 127?mm (5.00?in.) long sleeve was placed in the hammer mechanism to reduce the drop height from 762?mm (30?in.) to 635?mm (25in.). To calibrate the energy for these drop heights, measurements were made for a series of SPT tests in Borehole X2 at WLA on November 21, 2003. For these SPT, sleeves were inserted with lengths of 50?mm (2?in.), 127?mm (5?in.) 177?mm (7?in.), and no sleeve. Resulting drop heights were 762?mm (30?in.), 711?mm (28?in.), 635?mm (25?in.), and 584?mm (23?in.). Results indicate that: (1) ER increases with rod length as expected; (2) corrections for rod length, CR, increased with rod length in accordance with CR published in 2001 by Youd et al.; and (3) for lengths greater than 6?m, ER increased approximately linearly with drop height. Average ER30 [ER based on a 762?mm (30?in.) drop height] were 43% for a 584?mm (23?in.) drop, 60% for a 635?mm (25?in.) drop, 84% for 711?mm (28?in.) drop, and 89% for a 762?mm (30?in.) drop.