DYCOMS-II Satellite: TMMM TMI 3 Day Mean Data 1.0 General Information The TRMM TMI 3 Day Mean Data is one of several satellite data sets collected by the University Corporation for Atmospheric Research/Joint Office for Science Support (UCAR/JOSS) as part of the Dynamics and Chemistry of Marine Stratocumulus Phase II: Entrainment Studies (DYCOMS-II) project. Three day mean retrievals from the Tropical Rainfall Measurement Mission (TRMM) Microwave Imager (TMI) of sea surface temperature, surface wind speeds, atmospheric water vapor, liquid cloud water and precipitation rates are included in this data set. The data cover the period from 7 - 28 July 2001 and are in binary format on a 0.25 by 0.25 degree grid. The data were acquired from Remote Sensing Systems (http://www.ssmi.com/tmi_browse.html). 2.0 Data Contact Deborah Smith email: smith@remss.com phone: (707)545-2904 Ext. 11 (9 to 5:30 PST) Remote Sensing Systems has granted permission to publish the images from this data, when accompanied by the following statement: Data and images are produced by Remote Sensing Systems and sponsored, in part, by NASA's Earth Science Information Partnerships (ESIP): a federation of information sites for Earth science; and by the NOAA/NASA Pathfinder Program for early EOS products; principal investigator: Frank Wentz. 3.0 Data and Format Information 3.1 Introduction This data set offers geophysical parameters derived from observations made by a radiometer onboard the Tropical Rainfall Measuring Mission (TRMM) satellite. This radiometer, the TRMM Microwave Imager (TMI) is well-calibrated, similar to SSM/I and contains lower frequency channels required for sea surface temperature retrievals. The entire data set includes sea surface temperatures (SST), surface wind speeds derived using two different radiometer channels, atmospheric water vapor, liquid cloud water and precipitation rates. TRMM is a joint program between NASA and the National Space Development Agency of Japan (NASDA). All images cover a global region extending from 40S to 40N at a pixel resolution of 0.25 deg (25 km). Unlike SSM/I on DMSP platforms, the TRMM satellite travels west to east in a semi-equatorial orbit. This produces data collected at changing local times for any given earth location between 40S and 40N. The DMSP platforms are in a near-polar, sun-synchronous orbit. Therefore, the SSM/I instruments collect data daily at the same local time. Due to these orbital differences, we offer AM/PM maps of SSM/I data and ascending/descending maps of TRMM data. The production of this data set is a collaborative effort with the TRMM Project at GSFC and the Passive Microwave Earth Science Information Partnership (ESIP) for Climate Studies. The Passive Microwave ESIP is a newly established data center that will be providing climate products derived from satellite microwave radiometers and is a joint effort among NASA's Global Hydrology and Climate Center, the University of Alabama in Huntsville, and Remote Sensing Systems. The scientists working on the TRMM SST algorithm and analysis are Frank Wentz, Chelle Gentemann, and Deborah Smith of Remote Sensing Systems. 3.2 Sea Surface Temperatures The measurement of sea-surface temperature through clouds by satellite microwave radiometers has been an elusive goal for many years. The early radiometers in the 1980's (i.e., SMMR) were poorly calibrated, and the later radiometers (i.e., SSM/I) lacked the low frequency channels needed by the retrieval algorithm. Finally, in November 1997, the TMI radiometer with a 10.7 GHz channel was launched aboard the TRMM satellite. The important feature of microwave retrievals is that SST can be measured through clouds, which are nearly transparent at 10.7 GHz. This is a distinct advantage over the traditional infrared SST observations that require a cloud-free field of view. Ocean areas with persistent cloud coverage can now be viewed on a daily basis. Furthermore, microwave retrievals are not affected by aerosols and are insensitive to atmospheric water vapor. However, the microwave retrievals are sensitive to sea-surface roughness, while the infrared retrievals are not. A primary function of the TRMM SST retrieval algorithm is the removal of surface roughness effects. The microwave and infrared SST retrievals are very complementary and can be combined to obtain a reliable global data set. The algorithm for retrieving SST's from radiometer data is described in "AMSR Ocean Algorithm" at http://www.ssmi.com/papers/OCEANATBD.PDF We have significantly improved the SST data first made available on this web site in July 1998. The day to day variations in the SST images have been reduced and obvious striping along swath edges removed. The SST binary data are now available as part of the 7 parameter binary data file described below. We invite comments, suggestions, and critiques. Please address SST e-mail to gentemann@remss.com or sign our guestbook. 3.3 Other Geophysical Parameters In addition to SST retrievals, we are able to obtain from the TMI data surface wind speeds, atmospheric water vapor, liquid cloud water and precipitation rates. The algorithms used to retrieve the data are those used in SSM/I data processing. These algorithms are described in "A Well Calibrated Ocean Algorithm for SSM/I " - PS format (http://www.ssmi.com/papers/ssmi.ps) or PDF format (http://www.ssmi.com/papers/ssmi.pdf). Appropriate adjustments have been made to account for small differences in GHz between the TMI and SSM/I channels and for the fact that TMI water vapor is measured at 21 GHz rather than 22.235 GHz as in all SSM/I. In addition, small offsets are added to the TMI antenna temperatures in order to intercalibrate them with the SSM/I instrument series. Two surface wind speed retrievals are provided in this data set. The first is a surface wind speed derived primarily from the 11 GHz channel available only on TMI. The second surface wind speed retrieval relies on measurements made by the 37 GHz channels and uses the SSM/I algorithm. A cursory inspection suggests that these two products are very similar. We encourage users to compare the two products and provide us with feedback. Please address wind e-mail to smith@remss.com or sign our guestbook. Like the sea surface temperature maps, the 11GHz surface wind speed maps have small regions of missing data that occur. These regions are located where the sunlight reflects off the ocean surface (also called "sun glint") and affects the 11 GHz channel. Where this occurrs, the data are removed. 3.4 Binary Data Files Each 3-DAY binary data file consists of six 0.25 x 0.25 degree grid (1440,320) byte maps. Six ascending maps in the following order, Sea Surface Temperature (S), 10-meter Surface Wind Speed using 11 GHz (Z), 10-meter Surface Wind Speed using 37 GHz (W), Atmospheric Water Vapor (V), Cloud Liquid Water (L), and Precipitation Rate (R) are followed by six descending maps in the same order. There are two cases for which neighboring data swaths overlap. At higher latitudes, orbit segments overlap within local regions and within a short measurement time. In these cases, parameter data are averaged. In the second case, there is a "seam" on each map where the first and last orbit segments of the day overlap. Data at this seam are not averaged. Here, later swath data overwrite data previously measured at the beginning of the day. The center of the first cell of the 1440 column and 320 row map is at 0.125 E longitude and -39.875 latitude. The center of the second cell is 0.375 E longitude, -39.875 latitude. The data values fall between 0 and 255. Specific values have been reserved: 255 = land mass 254 = no TMI observations 253 = TMI observations exist, but are bad 252 = * not used in this data set* 251 = missing wind speed due to rain, or missing water vapor due to heavy rain 0 to 250 = valid geophysical data The data values between 0 and 250 need to be scaled to obtain meaningful geophysical data. To scale the data, multiply by the scale factors listed below: T: multiply by 6.0 to get minute GMT between 0 and 1440 S: multiply by 0.15 AND subtract 3 to get SST between -3 and 34.5 C Z: multiply by 0.15 to get 10 m winds between 0 and 37.5 m/sec W: multiply by 0.15 to get 10 m winds between 0 and 37.5 m/sec V: multiply by 0.3 to get water vapor between 0 and 75 mm L: multiply by 0.01 to get cloud liquid water between 0 and 2.5 mm R: multiply by 0.1 to get rain between 0 and 25 mm/hr 3.5 Programs For Reading Files Fortran, IDL and Matlab programs for reading these data files are available from Remote Sensing Systems at ftp://ftp.ssmi.com/TMI/TMI_support/ Remote Sensing Systems also would like to receive notice when these images are used in publications. Please send a note to Sharon Tremble (tremble@remss.com), informing us of the journal and expected publication date. It would also be greatly appreciated if you could send a reprint to us. The address is 438 First Street, Suite 200, Santa Rosa, CA 95401, USA. 4.0 Quality Control Procedures UCAR/JOSS conducted no quality checks on these data. 5.0 File Naming Convention The file names are structured as follows: trmm_yyyymmdd_tmi_3day Where trmm is the satellite used yyyy is the four digit year mm is the two digit month dd is the two digit day tmi_3day is the name of the data set 6.0 References None