TITLE: Aircraft C-130 Radiation TDDR Measurements (Valero) AUTHOR(S): PI: Francisco P.J. Valero University of California, San Diego Scripps Institution of Oceanography 9500 Gilman Drive, Dept 0242 La Jolla, CA 92092-0242 Phone: 858-534-2701 FAX: 858-822-0517 email: fvalero@ucsd.edu Co-PI: Brett C. Bush (Same address as above) Phone: 858-822-0514 email: bcbush@ucsd.edu Co-PI: Shelly K. Pope (Same address as above) Phone: 858-534-9619 email: spope@ucsd.edu 1.0 DATA SET OVERVIEW: This data set contains radiation measurements made during ACE-ASIA on the C-130 aircraft. Archived data consists of two spectral narrowband radiometers (one uplooking and one downlooking). Each TDDR (Total-Direct-Diffuse Radiometer) had a hemispherical field-of-view, and a scanning shadowband was used (only on the uplooking instrument) to regularly block the sun thus allowing determination of the total, direct, and diffuse components of the radiation field. The TDDR consisted of seven unique channels measuring the following spectral regions: 495-505 nm, 400-450 nm, 450-500 nm, 500-550 nm, 550-600 nm, 600-650 nm, and 650-700 nm. RAMS measurements on the NCAR C-130 were made on each of the research flights during the intensive field phase of ACE-ASIA in 2001: March 31 April 2, 4, 6, 8, 11, 12, 13, 17, 18, 20, 23, 24, 25, 27, 30 May 1, 2, 4 2.0 INSTRUMENT DESCRIPTION: The accuracy of the TDDR measurements is typically 3%. The uplooking instrument has had navigation corrections applied that are functions of the aircraft pitch, roll, and heading. These corrections are made to account for any mounting offsets between the radiometers and the aircraft as well as relate the measurements to a level platform. All radiometric measurements are acquired at approximately 5Hz. Note: the "dips" present in the uplooking TDDR measurements correspond to the time when the shadowband is blocking the direct sunlight from hitting the detector. 3.0 DATA COLLECTION AND PROCESSING: All radiometric measurements are acquired using the RAdiation Measurement System (RAMS). The raw measurements are converted to fluxes using the following steps, briefly summarized below: 1) Subtract "dark" signal 2) Apply calibration constant 3) Correct downwelling fluxes for slight deviations of the angular response from an ideal cosine using estimates of the direct:total ratio as well as the aircraft attitude. Data quality control consists of eliminating periods of data deemed unsuitable for flux measurements (i.e. warm up periods, large pitch and roll excursions, etc.) Although not released in the accompanying data files, aerosol optical depths are calculated from the uplooking TDDR measurements (in cloudless conditions) using a shadowband analysis developed at the Atmospheric Research Laboratory, Scripps Institution of Oceanography, University of California, San Diego. Anyone interested in obtaining these calculations should contact the PI or either one of the Co-PIs listed above. 4.0 DATA FORMAT: All data is archived in NetCDF format. A list of the variables is summarized below: base_time - "seconds since 00:00:00 1 Jan 1970 GMT" ; time_offset - "seconds since base time" ; Zen_wavelength - "Nominal Central Wavelength of Zenith TDDR Spectral Channel (nm)" Zen_bandwidth - "Nominal Bandwidth of Zenith TDDR Spectral Channel (nm)" Nad_wavelength - "Nominal Central Wavelength of Nadir TDDR Spectral Channel (nm)" Nad_bandwidth - "Nominal Bandwidth of Nadir TDDR Spectral Channel (nm)" Zen_TDDR - "ARL-Scripps Zenith Total-Direct-Diffuse Radiometer (W/m2/nm)" Nad_TDDR - "ARL-Scripps Nadir Total-Direct-Diffuse Radiometer (W/m2/nm)" The "base_time" variable is always defined to be an integral number of whole days so that all time offset is also the offset from 00:00:00 GMT on the given measurement day. (Note: because the GMT day changed during some of the research flights, it is possible to have "negative" times.) Bad TDDR fluxes are flagged with a value of "-99.999". 5.0 DATA REMARKS: Any questions or comments regarding this data set should be addressed to the the PI or Co-PIs listed at the top of this README file. 6.0 REFERENCES: TDDR Reference: Valero and Pilewskie, 1992, Latitudinal Survey of Spectral Optical Depths of the Pinatubo Volcanic Cloud, Geophysical Research Letters 19,p. 163