--------------------------------------------------------------------------------------- --------------------------------------------------------------------------------------- October 12, 2017 This directory contains collocated observations between ship observations taken from the Rvflux-2.0 data set derived from SAMOS ship observations and satellite observations from the DMSP SSM/I and SSMIS instruments and AMSU-A observations from NOAA and Metop satellites. Details on the file naming convention, the date record format, and further details on the collocation technique are given below. --------------------------------------------------------------------------------------- FILE NAME CONVENTION The file names having the following format: ___.dat where ship -> ship ID flux_model -> B12 = Flux model based on Bourassa et al. (1999), Bourassa (2006), and Zheng et al. (2013) begin year - end year -> time range of collocations sky_condition -> clear = clear-sky, cloud = cloudy-sky --------------------------------------------------------------------------------------- DATA RECORD yyddd,fhour,lat,lon,qa,ta,ssmi_sat_id, del_t1, del_s1, tb19v, tb19h, tb22v, tb37v, tb37h, amsu_sat_id, del_t2, del_s2, tb52, tb53, tb54 where yyddd -> two digit year + 3 digit day of year fhour -> time of day in fractional hours lat -> ship latitude in degrees (-90 to 90) lon -> ship longitude in degrees (0 - 359.99) qa -> ship 10 m specific humidity ta -> ship 10 m air temperature ssmi_sat_id -> SSMI or SSMIS satellite ID (i.e. F13 = DMSP F13 satellite) del_t1 -> time difference between SSMI/ship (sat-ship) in fractional hours del_s1 -> space difference between center of SSMI footprint and ship (sat-ship) in km. tb19v -> brightness temperature in Kelvin for v-polarized 19 GHz channel tb19h -> brightness temperature in Kelvin for h-polarized 19 GHz channel tb22v -> brightness temperature in Kelvin for v-polarized 22 GHz channel tb37v -> brightness temperature in Kelvin for v-polarized 37 GHz channel tb37h -> brightness temperature in Kelvin for h-polarized 37 GHz channel amsu_sat_id -> AMSU-A satellite ID (i.e. M02 = Metop-2, N18 = NOAA-18) del_t2 -> time difference between AMSU/ship (sat-ship) in fractional hours del_s2 -> space difference between center of AMSU footprint and ship (sat-ship) in km. tb52 -> brightness temperature in Kelvin for 52.8 GHz temperature channel tb53 -> brightness temperature in Kelvin for 53.6 GHz temperature channel tb54 -> brightness temperature in Kelvin for 54.4 GHz temperature channel --------------------------------------------------------------------------------------- BACKGROUND INFORMATION SSMI/SSMIS and AMSU satellite observations were collocated with SAMOS ship observations for the period from 2005 through 2014. Here is a description of the steps performed to construct the collocated data. Ship observations originate from the SAMOS data archive (samos.coaps.fsu.edu/html/data_availability.php) from which the Rvflux-2.0 data set (onlinelibrary.wiley.com/doi/10.1002/gdj3.34/full#references) was derived and contained height-corrected Ta and Qa ship observations to 10 m using an updated variant of the Bourassa 1999 flux model. 1-minute ship observations were collocated to inter-calibrated satellite observations with a less than 3 hour time requirement between ship and satellite data. The spatial difference between ship and satellite was less than 50 km spatial requirement for AMSU and less than 25 km spatial requirement for SSMI. The larger spatial requirement for AMSU accommodated the larger footprint size of those data. The collocated ship/satellite data were filtered for possible land contamination of the satellite observations using a 1/16 of a degree land mask. Each collocated data record was assigned a minimum distance that the satellite observation was from land. Land contamination is defined as minimum distances of 40 km between the center location of the satellite observation and nearest land. For far limb AMSU observations (positions 1-4, 26-30), the distance is increased to 80 km since the AMSU footprint becomes large at the far limb. Furthermore, each data record was assigned a cloud liquid water (CLW) and rain rate (RR) value taken from the Remote Sensing Systems version 7 retrievals which were derived from SSM/I observations. The next step combines coincident ship/AMSU and ship/SSMI data records into data records containing match ship/AMSU/SSMI observations. Land contaminated data records are removed and data records are separated into clear-sky and cloudy-sky collocated data using the CLW and RR data. Clear-sky is defined as observation with CLW < 0.025 mm and RR = 0 mm/hr, and cloudy-sky is defined as 0.025 mm < CLW < 0.25 mm and RR = 0 mm/hr. All rain conditions (RR > 0 mm/hr) were removed from the collocated data. Collocated ship, SSMI, and AMSU data records were constructed by finding the satellite observation, for both SSMI and AMSU, with the minimum time difference for each satellite for each 1-minute ship observation. However, generally 1-minute ship observations result in a number of redundant collocated satellite observations since one satellite footprints collocates with more than one ship observation. Therefore, a further reduction of the collocated data was performed by eliminating these redundant satellite observations by finding the footprint that matches most closely in time with a set of ship observations. Also, redundant satellite observations between the SSM/I and AMSU were eliminated by finding ship observation that minimizes the total time difference from both instruments. The final matched data set of ship and satellite data contains 47,353 clear-sky and 40,802 cloud-sky collocated data records spanning over a nearly 10-year time period and diverse regions of the global oceans. ---------------------------------------------------------------------------------------------- Questions regarding these data should be directed to Darren Jackson at Darren.L.Jackson@noaa.gov ---------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------------------