Langley DAAC Version Number: LD_008_006_001_00_00_0_19990621 FIRE_ACE_UWCV580_GMETER Readme 1.0 Introduction This file contains information about the data provided by the g-meter instrument flown onboard the University of Washington's CV580 aircraft during the FIRE ACE field campaign. It includes implementation of the sample READ software. This data set is available through the Langley Atmospheric Sciences Data Center as: FIRE_ACE_UWCV580_GMETER Each granule contains one flight of data in ASCII format. The data represent 100-point running averages for flights up to and including June 5, 1998 and 13-point running averages for the remaining flights. All data segments were chosen to include cloud. This Readme file includes the following sections: Section 2.0 - Data Set Description Section 3.0 - Data Format and Packaging Section 4.0 - Science Parameter Information Section 5.0 - Description of Sample Read Software Section 6.0 - Implementing Sample Read Software Section 7.0 - Sample Output Section 8.0 - Additional Information If there are questions about using the FIRE_ACE_UWCV580_GMETER sample read software, please contact the Langley Science User and Data Services (SUDS) office at: Langley Atmospheric Sciences Data Center NASA Langley Research Center Mail Stop 157D, 2 S. Wright St. Hampton, VA 23681-2199 USA E-Mail: larc@eos.nasa.gov Phone: (757)864-8656 FAX: (757)864-8807 2.0 Data Set Description 2.1 Instrument Description A four-channel integrating nephelometer, termed a "g-meter" for short, was mounted on the University of Washington CV-580 aircraft during the FIRE ACE field campaign. The g-meter measures the following light scattered (at a wavelength of 635 nm) by cloud hydrometeors in a volume of about 300 liters/sec.: F = forward scattered light (10 deg. - 90 deg.) B = back scattered light (90 deg. - 175 deg.) cosF = forward scattered light times the cos of the scattering angle (10 deg. to 90 deg.) cosB = back scattered light times the cos of the scattering angle (90 deg. - 175 deg.) 2.2 Raw Data The 4 g-meter outputs were recorded by a dedicated DAQBOOK data logger and laptop computer at 100 Hz. One channel (F) stopped functioning starting on flight no. 1762, June 6. The laptop experienced a fatal hard-disk crash on the next flight. A copy of the raw 100-Hz g-meter data, including offset adjustment values, is available upon request from Dr. Hermann Gerber (see section 2.4 for complete contact information). The g-meter outputs were also recorded by the University of Washington CV-580 data logger at 13 Hz. Data were collected on all flights. 2.3 Data Reduction 2.3.1 100-Hz DAQBOOK data for flights up to and including June 5: The data are smoothed with a 100-pt running average, and then the following 3 quantities are calculated: g = asymmetry parameter g = [f x (F + B) + (cosF - cosB) x (1 - f)]/(F + B); e = extinction coefficient (1/Km) e = (F + B)/(1 - f) ; eBr = extinction-to-backscatter ratio eBr = e/B ; br = backscatter ratio br = 1/[eBr x (1 + dt)] where dt is approximately 0.1. The fraction of light diffracted by the hydrometeors is given by f (see Gerber, H., 1996: "Measurement of the asymmetry parameter and optical extinction coefficient of ice crystals and water droplets". Final Report NAS1-20506, NASA Langley Research Center, Hampton, VA). The value of f used in all the archived data is 0.53. Data accuracy is improved by using a value of f = 0.52 for clouds containing only liquid water, and by using a value of f = 0.57 for clouds containing only ice. For ice clouds the value of g must be increased by a maximum amount of 0.03 to account for the "delta transmission" when the ice crystals contain parallel facets with no inclusions or imperfections. For additional discussion of the variability of f and g see Gerber, H., et al., 1999; "Nephelometer measurements of the asymmetry parameter, volume extinction coefficient and backscatter ratio in Arctic clouds"; Journal of The Atmospheric Sciences.) 2.3.2 13-Hz CV-580 logger data: The 13 Hz data is smoothed with a 13-pt. running average and then the following quantity is calculated from the cosF channel of the g-meter for flights starting on June 6: e = extinction coefficient (1/Km) e = (F + B)/(1 - f) ; (1) where average F/cosF = 1.300 (std dev. = 0.056) (2) average e/B = 23.8 (std dev. = 5.3) (3); where the average values represent all the g-meter data collected with the DAQBOOK inclusive of the flights to June 5. Combining (1) to (3) yields e = [(cosF x 1.300) + B]/(1 - f) , where B = (cosF x 1.300)/[23.8 x (1 - f) -1]. 2.3 Calibration and Accuracy The relative calibration of the 4 diffuser/photomultipier assemblies in the g-meter was accomplished by exposing the assemblies simultaneously to the same light source. The "absolute" calibration of the 4 channels of the g-meter was accomplished by operating the g-meter co-located with a PVM-100A in a cloud chamber. The surface area channel(PSA) of the PVM is directly related to the total scattered light(e) of the g-meter under the condition that the droplets in the cloud fall within the operating range of each instrument. The calibration of the LWC and PSA channels of the PVM is traceable to comparisons with a reference LWC method in the Petten, The Netherlands cloud chamber; and to comparisons with monodisperse glass beads in a vertical fall tunnel. The absolute calibration of the g-meter with the PVM has an accuracy estimated at +/-15%. The unknown value for Qscat for the small droplets used in the calibration is the reason for the increased uncertainty. 2.4 Science Point of Contact Dr. Hermann E. Gerber Gerber Scientific Inc. 1643 Bentana Way Reston, VA 20190 USA E-mail: gerber.gsi@erols.com Phone: 703-742-9844 Fax: 703-742-3374 3.0 Data Format and Packaging The data for one flight are contained in several files. The individual files have been "zipped" into one file that covers the entire flight. 3.1 ZIP information To unzip the files with Info-Zip software, download the freeware and information from the following URL: http://www.cdrom.com/pub/infozip/ 3.2 Data Format The data are in ASCII format. They have been averaged according to the procedures discussed in section 2.3 above. 3.3 File Naming Convention: The FIRE_ACE_UWCV580_GMETER data granules are prefixed with "fire_ace_uwcv580_gmeter_" to indicate they belong to this data set. An eight digit date follows the prefix and it indicates the year, month and day of flight. The filename is completed with a ".zip" extension. When these files are unzipped all the files obtained during a flight are provided. These file names have a numerical extention indicating the order of the data files. Example zip file name: fire_ace_uwcv580_gmeter_19980520.zip Gmeter data taken May 20, 1998 Example data file names: fire_ace_uwcv580_gmeter_19980520_01 All of the data files for the fire_ace_uwcv580_gmeter_19980520_02 flight on May 20, 1998 fire_ace_uwcv580_gmeter_19980520_03 fire_ace_uwcv580_gmeter_19980520_04 fire_ace_uwcv580_gmeter_19980520_05 fire_ace_uwcv580_gmeter_19980520_06 fire_ace_uwcv580_gmeter_19980520_07 fire_ace_uwcv580_gmeter_19980520_08 4.0 Science Parameter Information The data parameters for all flights up to and including June 5, 1998 are: Parameter Description (units) t(s) local start time of the segment in seconds, g asymmetry parameter, e extinction coefficient (1/km) e/b extinction-to-backscatter ratio The data parameters for the remaining flights are: Parameter Description (units) UW time University of Washington time (UTC) e extinction coefficient (1/Km) 5.0 Description of Sample Read Software Currently, there is one sample read program which works with the FIRE_ACE_UWCV580_GMETER data set, read_gmeter.c. It is written in the C programming language. This program has been tested on the following computers and operating systems: Computer Operating System ------------------- ---------------- Sun Sparc Solaris 2.6 SGI Origin 2000 IRIX 6.4 HP 9000/735 HP-UX 10.10 This program is written as an example of how to read in the GMETER data. As delivered, it prompts the user for input and output filenames, and parameters to output. It reads in the entire file and writes to the output file the data as selected by the user. 6.0 Implementing the Sample Read Software 6.1 Compiling the Sample READ Software To compile the program, use the command for the C compiler. The command may vary slightly among operating systems, "cc", "acc", "gcc". On most systems the command is: % cc -o read_gmeter read_gmeter.c where: % - unix command line prompt cc - the C compiler -o - compiler option to create an executable filename read_gmeter - the executable filename read_gmeter.c - the source filename No libraries need to be linked to run this program. If the appropriate compile command is not found on your system, check to be sure that your PATH environment variable includes the directory that contains the compiler or specify the entire path to the compiler in your command. This compile command creates an executable program file named read_gmeter. 6.2 Running the Sample READ Software To execute the GMETER read program, type: % read_gmeter The user is then prompted by the program to enter the filename of interest. 7.0 Sample Output The read_gmeter.c program can be used to read any of the GMETER data files. The following is a sample session showing compilation and execution of the program. % cc read_gmeter.c -o read_gmeter % read_gmeter **************************************************************** * * * * * FIRE_ACE_UWCV580_GMETER Read Software * * * * Version: 1.0 * * * * Date: August 10, 1999 * * * * Contact: Science User and Data Services Office * * Langley Atmospheric Sciences Data Center * * NASA Langley Research Center * * Mail Stop 157D, 2 S. Wright St. * * Hampton, VA 23681-2199 * * USA * * * * E-mail: larc@eos.nasa.gov * * Phone: (757)864-8656 * * FAX: (757)864-8807 * * * * * **************************************************************** Please enter the name of the INPUT file you wish to read : NOTE: Data file may be in the current working directory, or enter the complete pathname for the data filename. fire_ace_uwcv580_gmeter_19980520_06 Please enter the name of the OUTPUT file: output ************************************************************* * WARNING: This filename exists: output * Do you wish to overwrite it? 'y' yes 'n' no * ************************************************************* y Here is the GMETER parameter list: NUM. NAME UNITS -------------------------------------- 1. T Sec. 2. G n/a 3. E (1/Km) 4. E/B n/a Enter 'a' to process all the data parameters. Enter 's' to select the number(s) for the parameter(s) to process. Enter 'h' to receive help with commands. Enter 'x' to exit or terminate processing. s How many parameters would you like printed out with each record? NOTE: maximum number of parameters is 4 Please enter your selection now: (1 - 4) 3 Enter the parameter(number) you wish for column #1. 1 Enter the parameter(number) you wish for column #2. 2 Enter the parameter(number) you wish for column #3. 4 You have requested the following parameters to process: T(S) 1 G 2 E/B 4 If you are dissatisfied with your selections enter any value other than 'q' or 'x' to reenter your selection Enter 'x' to exit the program. Enter 'q' or 'quit' to begin processing your selections. q --------------------------------------------------------- ~ End of file has been reached with 3000 records ~ read in from the data file: fire_ace_uwcv580_gmeter_19980520_06 ~ Program has completed successfully! --------------------------------------------------------- Sample output file: T(Sec) G E/B Sec. n/a n/a 0.0000 0.8790 14.3070 0.1000 0.8720 15.7150 0.2000 0.8680 18.4940 0.3000 0.8640 21.9220 0.4000 0.8570 25.5390 0.5000 0.8490 31.0660 0.6000 0.8440 33.6370 etc ... 299.4000 0.8680 29.1660 299.5000 0.8410 23.6470 299.6000 0.8060 17.3970 299.7000 0.7770 14.7120 299.8000 0.7500 11.9410 299.9000 0.7350 10.5560 8.0 Additional Information The files listed below, up to and including June 5, 1998, each consist of a 5-min. segment of 10-Hz data (g, e, and e/B) selected from a 100-pt. running average of the DAQBOOK 100-Hz data. All segments were chosen to include cloud. The time listed is local time of the start of the segment as indicated by the DAQBOOK logger. The files listed from June 6, 1998 on, consist of cloud segments of 13-Hz data (e) from a 13-pt running average of 13-Hz CV-580 logger data. The time of the start of the segment listed is Universal Time as indicated by the CV-580 logger. A "?" in the table below, indicates questionable data quality. Filename Start Time mean mean mean Quality (hh:mm:ss) g e e/B FLIGHT 1751, MAY 20 (1/Km) fire_ace_uwcv580_gmeter_19980520_01 12:35:30 .847 52.6 28.4 fire_ace_uwcv580_gmeter_19980520_02 12:40:29 .824 43.9 23.0 fire_ace_uwcv580_gmeter_19980520_03 12:45:29 .825 23.5 22.0 fire_ace_uwcv580_gmeter_19980520_04 13:30:29 .854 67.2 33.7 fire_ace_uwcv580_gmeter_19980520_05 13:35:29 .844 57.8 27.8 fire_ace_uwcv580_gmeter_19980520_06 13:40:29 .842 57.1 32.6 fire_ace_uwcv580_gmeter_19980520_07 13:45:29 .857 24.4 28.6 fire_ace_uwcv580_gmeter_19980520_08 15:32:47 .846 42.7 29.3 FLIGHT 1752, MAY 21 fire_ace_uwcv580_gmeter_19980521_01 12:31:30 .816 23.3 17.4 fire_ace_uwcv580_gmeter_19980521_02 12:46:30 .875 28.4 36.1 ? fire_ace_uwcv580_gmeter_19980521_03 12:51:30 .883 14.0 21.5 ? fire_ace_uwcv580_gmeter_19980521_04 13:51:31 .852 32.4 27.3 FLIGHT 1753, MAY 23 fire_ace_uwcv580_gmeter_19980523_01 11:27:14 .822 39.1 25.4 fire_ace_uwcv580_gmeter_19980523_02 11:47:55 .805 19.1 21.1 fire_ace_uwcv580_gmeter_19980523_03 11:52:54 .806 22.2 21.6 fire_ace_uwcv580_gmeter_19980523_04 11:57:55 .839 16.0 27.2 fire_ace_uwcv580_gmeter_19980523_05 12:07:55 .830 26.1 20.2 fire_ace_uwcv580_gmeter_19980523_06 12:22:55 .822 21.5 21.6 fire_ace_uwcv580_gmeter_19980523_07 12:27:55 .851 30.8 27.2 fire_ace_uwcv580_gmeter_19980523_08 12:32:55 .840 28.3 25.1 FLIGHT 1754, MAY 27 fire_ace_uwcv580_gmeter_19980527_01 15:31:37 .787 12.3 16.8 fire_ace_uwcv580_gmeter_19980527_02 15:36:37 .730 17.5 10.6 ? fire_ace_uwcv580_gmeter_19980527_03 15:56:37 .810 16.7 19.2 ? fire_ace_uwcv580_gmeter_19980527_04 16:01:37 .835 12.9 22.6 FLIGHT 1755, MAY 28 fire_ace_uwcv580_gmeter_19980528_01 12:37:05 .887 14.3 29.9 ? fire_ace_uwcv580_gmeter_19980528_02 13:47:09 .785 9.84 16.1 fire_ace_uwcv580_gmeter_19980528_03 13:52:09 .813 21.9 19.0 fire_ace_uwcv580_gmeter_19980528_04 13:57:09 .797 27.2 18.7 fire_ace_uwcv580_gmeter_19980528_05 14:02:09 .844 22.2 24.8 fire_ace_uwcv580_gmeter_19980528_06 19:07:09 .761 15.5 12.8 ? FLIGHT 1756, MAY 29 fire_ace_uwcv580_gmeter_19980529_01 11:33:12 .812 14.5 19.0 ? FLIGHT 1757, MAY 30 fire_ace_uwcv580_gmeter_19980530_01 13:24:47 .829 55.1 29.6 fire_ace_uwcv580_gmeter_19980530_02 13:29:46 .808 12.4 19.9 fire_ace_uwcv580_gmeter_19980530_03 14:24:47 .812 26.6 19.2 fire_ace_uwcv580_gmeter_19980530_04 14:24:47 .853 27.7 32.6 fire_ace_uwcv580_gmeter_19980530_05 14:44:46 .839 20.9 27.0 fire_ace_uwcv580_gmeter_19980530_06 14:49:46 .798 23.9 24.5 FLIGHT 1758, JUNE 1 fire_ace_uwcv580_gmeter_19980601_01 16:01:31 .693 16.3 8.81 fire_ace_uwcv580_gmeter_19980601_02 16:21:31 .809 23.4 19.2 ? FLIGHT 1759, JUNE 2 fire_ace_uwcv580_gmeter_19980602_01 13:33:31 .847 22.0 28.6 ? fire_ace_uwcv580_gmeter_19980602_02 13:38:31 .797 12.7 14.9 ? fire_ace_uwcv580_gmeter_19980602_03 13:43:31 .828 42.2 24.5 fire_ace_uwcv580_gmeter_19980602_04 14:33:31 .817 18.1 20.4 fire_ace_uwcv580_gmeter_19980602_05 14:43:31 .764 21.8 13.2 fire_ace_uwcv580_gmeter_19980602_06 14:48:31 .762 28.0 14.8 fire_ace_uwcv580_gmeter_19980602_07 14:53:31 .834 33.9 24.3 ? FLIGHT 1760, JUNE 3 fire_ace_uwcv580_gmeter_19980603_01 13:17:06 .855 30.7 34.0 fire_ace_uwcv580_gmeter_19980603_02 14:17:07 .849 16.4 24.6 fire_ace_uwcv580_gmeter_19980603_03 14:22:07 .821 17.3 20.4 ? fire_ace_uwcv580_gmeter_19980603_04 14:27:07 .807 23.6 17.9 ? fire_ace_uwcv580_gmeter_19980603_05 14:32:07 .805 17.5 24.0 fire_ace_uwcv580_gmeter_19980603_06 15:47:07 .805 11.0 20.6 fire_ace_uwcv580_gmeter_19980603_07 15:52:02 .821 22.2 25.7 fire_ace_uwcv580_gmeter_19980603_08 15:57:07 .840 22.0 26.7 FLIGHT 1761, JUNE 5 fire_ace_uwcv580_gmeter_19980605_01 14:23:22 .868 31.1 32.2 fire_ace_uwcv580_gmeter_19980605_02 14:28:22 .870 18.8 29.4 fire_ace_uwcv580_gmeter_19980605_03 16:43:22 .866 41.6 38.3 fire_ace_uwcv580_gmeter_19980605_04 16:48:22 .860 39.0 32.7 fire_ace_uwcv580_gmeter_19980605_05 16:53:22 .851 38.4 29.5 fire_ace_uwcv580_gmeter_19980605_06 16:58:22 .857 43.6 31.3 fire_ace_uwcv580_gmeter_19980605_07 17:03:22 .871 43.5 34.8 Filename Time mean Quality (hh:mm:ss) e FLIGHT 1762, JUNE 6 (1/Km) fire_ace_uwcv580_gmeter_19980606_01 19:39:59 31.5 fire_ace_uwcv580_gmeter_19980606_02 20:07:59 27.8 fire_ace_uwcv580_gmeter_19980606_03 20:33:57 21.8 fire_ace_uwcv580_gmeter_19980606_04 21:12:56 31.1 fire_ace_uwcv580_gmeter_19980606_05 21:59:00 37.3 fire_ace_uwcv580_gmeter_19980606_06 23:08:00 50.1 FLIGHT 1763, JUNE 7 fire_ace_uwcv580_gmeter_19980607_01 20:26:58 22.1 fire_ace_uwcv580_gmeter_19980607_02 20:33:59 41.1 fire_ace_uwcv580_gmeter_19980607_03 20:49:59 40.6 fire_ace_uwcv580_gmeter_19980607_04 21:56:59 25.1 fire_ace_uwcv580_gmeter_19980607_05 22:12:59 19.4 fire_ace_uwcv580_gmeter_19980607_06 23:11:59 15.9 FLIGHT 1764, JUNE 9 fire_ace_uwcv580_gmeter_19980609_01 20:02:00 52.8 fire_ace_uwcv580_gmeter_19980609_02 21:25:00 50.9 fire_ace_uwcv580_gmeter_19980609_03 22:07:00 28.1 FLIGHT 1765, JUNE 11 fire_ace_uwcv580_gmeter_19980611_01 18:10:00 31.4 fire_ace_uwcv580_gmeter_19980611_02 18:47:00 27.3 fire_ace_uwcv580_gmeter_19980611_03 19:02:17 30.1 fire_ace_uwcv580_gmeter_19980611_04 19:39:00 24.8 fire_ace_uwcv580_gmeter_19980611_05 20:14:00 35.4 FLIGHT 1766, JUNE 13 fire_ace_uwcv580_gmeter_19980613_01 20:04:52 66.1 fire_ace_uwcv580_gmeter_19980613_02 20:16:52 43.2 fire_ace_uwcv580_gmeter_19980613_03 20:54:01 23.8 fire_ace_uwcv580_gmeter_19980613_04 22:48:09 57.3 FLIGHT 1767, JUNE 14 fire_ace_uwcv580_gmeter_19980614_01 19:48:59 52.6 fire_ace_uwcv580_gmeter_19980614_02 20:15:37 44.6 fire_ace_uwcv580_gmeter_19980614_03 20:45:37 19.6 fire_ace_uwcv580_gmeter_19980614_04 21:19:00 31.9 fire_ace_uwcv580_gmeter_19980614_05 22:05:00 27.4 FLIGHT 1768, JUNE 18 fire_ace_uwcv580_gmeter_19980618_01 19:08:09 22.6 fire_ace_uwcv580_gmeter_19980618_02 21:18:00 25.5 fire_ace_uwcv580_gmeter_19980618_03 21:37:00 25.5 fire_ace_uwcv580_gmeter_19980618_04 23:56:50 77.6 fire_ace_uwcv580_gmeter_19980618_05 24:02:50 56.4 FLIGHT 1769, JUNE 19 fire_ace_uwcv580_gmeter_19980619_01 22:15:00 11.8 FLIGHT 1770, JUNE 22 fire_ace_uwcv580_gmeter_19980622_01 23:10:59 36.8 This file was last updated on August 4, 1999