The datasets below contain sea surface salinity retrieved by NASA’s Aquarius instrument collocated with in situ measurements by the Argo network of free drifting profiling floats. Sea surface salinity for Argo is defined as the shallower measurements reported by an Argo float as long as that measurement was reported for a depth of 10 m or less. Aquarius SSS, derived from L-band radiometry, are representative of the first few centimeters of the ocean surface layer. Collocations are reported in: One file containing all global collocations – Here Several regional files with collocations split by ocean basins as defined in the World Ocean Atlas (WOA) 2009 – Here The time period for the datasets covers the Aquarius mission lifetime: from August 25, 2011 to June 7, 2015. The Aquarius product version currently used in the datasets is V4.0 V5.0 [update: Sept 25, 2018](*). The file format is described below. The collocations are computed for various time windows (+/- 0.5, +/-3.5 and +/- 15 days) and distances (25 km, 75 km) around the Argo observation. Contact : Dr. Emmanuel Dinnat -- emmanuel.dinnat@nasa.gov (*) V4.0 of the data is still available on the server. V4.0 data are reachable by editing the URL of the link to a specific file, replacing "V5.0" with "V4.0". Aquarius Monthly Sea Surface Salinity (level 3) Global Dataset The global dataset contains about 500,000 collocations whose positions are reported in Fig. 1, with an average of about 11,000 collocations per month (Fig. 2). The spatial density of the collocations in 0.5° × 0.5° grid cells is shown in Fig. 3. Most sampled grid cells have just a few Argo observations (< 10 observations) with the exceptions of a few regions with much higher density (> 15 observations) in some coastal regions or in ocean gyres. Downloads: +/- 0.5 day25 km +/- 0.5 day75 km +/- 3.5 day25 km +/- 3.5 day75 km +/- 15 days25 km +/- 15 days75 km 6.3MB 18.8MB 39.5MB 95.5MB 47.9MB 105.0MB Fig. 1 Positions of individual Argo observations reported in the global dataset during the period Aug 25 2011 – June 07 2015. Fig. 2 Number of monthly Argo SSS observations versus time reported in the global dataset. Fig. 3 Density map of number of Argo measurements in 0.5° × 0.5° grid cells during the period Aug 25 2011 – June 07 2015. The colorscale is truncated for value 15 and above. Fig. 4 Histogram of the number of Argo measurements in 0.5° × 0.5° grid cells during the period Aug 25 2011 – June 07 2015. Regional Datasets The global dataset has been split in 14 regional datasets covering the various ocean basins as reported in Fig. 5. Fig. 5 Ocean Basins used for the regional collocation datasets. Basin definitions are from WOA 2009. Table 2 Ocean Basins definition in Fig. 5. 1 Atlantic Ocean 8 Persian Gulf 2 Pacific Ocean 9 Hudson Bay 3 Indian Ocean 10 Southern Ocean 4 Mediterranean Sea 11 Arctic Ocean 5 Baltic Sea 12 Sea of Japan 6 Black Sea 13 Caspian Sea 7 Red Sea 14 Bay of Bengal Downloads: +/- 0.5 day +/- 0.5 day +/- 3.5 day +/- 3.5 day +/- 15 days +/- 15 days 25 km 75 km 25 km 75 km 25 km 75 km 1 1.3MB 3.9MB 8.3MB 20.1MB 10.1MB 22.1MB 2 2.7MB 7.8MB 16.9MB 41.3MB 20.4MB 45.1MB 3 1.1MB 3.1MB 6.5MB 15.7MB 7.9MB 17.3MB 4 71.6KB 274.5KB 430.8KB 1.4MB 597.1KB 1.6MB 5 NA NA NA NA NA NA 6 NA NA 231B 233B 418B 544B 7 885B 2.2KB 5.0KB 14.0KB 6.6KB 17.1KB 8 NA NA NA NA NA NA 9 NA NA NA NA NA NA 10 884 KB 2.6MB 5.2MB 11.5MB 6.3MB 12.9MB 11 192KB 574.5KB 950.1KB 1.9MB 1.1MB 2.0MB 12 16.6KB 55.6KB 92.5KB 317.3KB 122.4KB 362.0KB 13 NA NA NA NA NA NA 14 74.6KB 226.4KB 461.2KB 1.1MB 609.9KB 1.3MB About Aquarius https://science.nasa.gov/mission/aquarius/ Aquarius was a NASA instrument dedicated to the measure of ocean surface salinity. It flown on the Aquarius/SAC-D mission and provided Sea Surface Salinity (SSS) retrievals between August 25, 2011 and June 7, 2015, until the mission’s ending due to a spacecraft failure [Lagerloef et al., 2008; Le Vine et al., 2015]. Aquarius used microwave radiometers at L-band (1.4 GHz) as its core instrument to retrieve SSS, with the help of an L-band radar scatterometer to correct for the impact of sea surface roughness on the radiometric observations. The radiometer had three beams pointing sideways of the spacecraft’s orbit. About Argo http://www.argo.net/ Argo is a global array of ~4,000 free-drifting profiling floats that measures temperature and salinity of the upper 2000 m of the ocean. Floats come back to the surface and vertically sample the ocean every ~10 days, with the shallowest measurement usually between 5 m and 10 m below ocean surface. The radiometric measurements by Aquarius are sensitive to salinity in the first few centimeters of the ocean, but the difference in depth between satellite and Argo measurements is negligible most of the time because the upper layer of the ocean is well mixed [Boutin et al., 2016]. At limited locations and times, with stratified upper layer due to rain events, differences between Argo and Aquarius observations due to difference in measurement depth are to be expected [Drucker and Riser, 2014]. File Content and Format The global and regional files share the same format. The files are in ASCII, compressed using zip. Every record (row) in the file is in reference to one Argo in situ observation. The first 14 fields (columns) for a record are information about the Argo observation. The rest of the records (columns 15 and higher) are information about Aquarius retrievals, collocated with the Argo observation. The first 14 fields, relating to the Argo observation, are given in Table 1 below. Salinity, Pressure, Depth and Temperature are given for the top two layers (Layer 1 is the shallowest measurement). When there is no valid observation of a parameter (col 7-14), a fill value of -1 is used. Table 1 First 14 fields of one record in the dataset related to the Argo observation 1 Date Date for Argo observation in format yyyymmddHHMMSS 2 Longitude Longitude for Argo observation between -180° and +180° 3 Latitude Latitude for Argo observation between -90° and +90° 4 File Number ID number of the Argo file *_prof.nc file containing the observation. File index is downloadable >> HERE << 5 Data Mode Indicates if the observation is real time, delayed mode or adjusted data 6 Platform ID World Meteorological Organization float identifier 7 Salinity Layer 1 Salinity observation at first (shallowest) depth (psu) 8 Pressure Layer 1 Pressure at first depth (dbar) 9 Depth Layer 1 Depth at first depth derived from Pressure (m) From [SBE, 2002] 10 Temperature Layer 1 Temperature at first depth (K) 11 Salinity Layer 2 Salinity observation at second depth (psu) 12 Pressure Layer 2 Pressure at second depth (dbar) 13 Depth Layer 2 Depth at second depth derived from Pressure (m) 14 Temperature Layer 2 Temperature at second depth (K) The next 120 fields are for Aquarius collocated data. The 120 fields are 30 variables repeated 4 times, once for each of the 3 Aquarius beams separately and a fourth time for all three beams combined. For examples, column 15 report the average of Aquarius SSS collocated with Argo considering only data from beam 1. Similarly, columns 16 and 17 consider only data from beam 2 and 3, respectively. Column 18 reports the average SSS from all beams combined. When no valid collocated value exists, a fill value of -1 is used. Aquarius SSS 15 SSS Aquarius Beam 1 16 SSS Aquarius Beam 2 17 SSS Aquarius Beam 3 18 SSS Aquarius all Beams 19 SSS Aquarius Beam 1 Ascending pass 20 SSS Aquarius Beam 2 Ascending pass 21 SSS Aquarius Beam 3 Ascending pass 22 SSS Aquarius all Beams Ascending pass 23 SSS Aquarius Beam 1 Descending pass 24 SSS Aquarius Beam 2 Descending pass 25 SSS Aquarius Beam 3 Descending pass 26 SSS Aquarius all Beams Descending pass Numerical model SSS HYCOM (psu) 27 SSS HYCOM Beam 1 28 SSS HYCOM Beam 2 29 SSS HYCOM Beam 3 30 SSS HYCOM all Beams Ancillary Data 31 SST NOAA Beam 1 (K) 32 SST NOAA Beam 2 (K) 33 SST NOAA Beam 3 (K) 34 SST NOAA all Beams (K) 35 Wind Speed Beam 1 (m/s) 36 Wind Speed Beam 2 (m/s) 37 Wind Speed Beam 3 (m/s) 38 Wind Speed all Beams (m/s) Statistics 39 Number of Aquarius footprints Beam 1 40 Number of Aquarius footprints Beam 2 41 Number of Aquarius footprints Beam 3 42 Number of Aquarius footprints all Beams 43 Number of Aquarius footprints Beam 1 Ascending 44 Number of Aquarius footprints Beam 2 Ascending 45 Number of Aquarius footprints Beam 3 Ascending 46 Number of Aquarius footprints all Beams Ascending 47 Number of Aquarius footprints Beam 1 Descending 48 Number of Aquarius footprints Beam 2 Descending 49 Number of Aquarius footprints Beam 3 Descending 50 Number of Aquarius footprints all Beams Descending 51 Standard Deviation Aquarius SSS Beam 1 (psu) 52 Standard Deviation Aquarius SSS Beam 2 (psu) 53 Standard Deviation Aquarius SSS Beam 3 (psu) 54 Standard Deviation Aquarius SSS all Beams (psu) 55 Standard Deviation Aquarius SSS Beam 1 Ascending (psu) 56 Standard Deviation Aquarius SSS Beam 2 Ascending (psu) 57 Standard Deviation Aquarius SSS Beam 3 Ascending (psu) 58 Standard Deviation Aquarius SSS all Beams Ascending (psu) 59 Standard Deviation Aquarius SSS Beam 1 Descending (psu) 60 Standard Deviation Aquarius SSS Beam 2 Descending (psu) 61 Standard Deviation Aquarius SSS Beam 3 Descending (psu) 62 Standard Deviation Aquarius SSS all Beams Descending (psu) Ice Contamination 63 Ice Fraction, mean, Beam 1 64 Ice Fraction, mean, Beam 2 65 Ice Fraction, mean, Beam 3 66 Ice Fraction, mean, all Beams 67 Ice Fraction, mean, Beam 1 Ascending 68 Ice Fraction, mean, Beam 2 Ascending 69 Ice Fraction, mean, Beam 3 Ascending 70 Ice Fraction, mean, all Beams Ascending 71 Ice Fraction, mean, Beam 1 Descending 72 Ice Fraction, mean, Beam 2 Descending 73 Ice Fraction, mean, Beam 3 Descending 74 Ice Fraction, mean, all Beams Descending 75 Ice Fraction, max, Beam 1 76 Ice Fraction, max, Beam 2 77 Ice Fraction, max, Beam 3 78 Ice Fraction, max, all Beams 79 Ice Fraction, max, Beam 1 Ascending 80 Ice Fraction, max, Beam 2 Ascending 81 Ice Fraction, max, Beam 3 Ascending 82 Ice Fraction, max, all Beams Ascending 83 Ice Fraction, max, Beam 1 Descending 84 Ice Fraction, max, Beam 2 Descending 85 Ice Fraction, max, Beam 3 Descending 86 Ice Fraction, max, all Beams Descending 87 Ice Fraction, min, Beam 1 88 Ice Fraction, min, Beam 2 89 Ice Fraction, min, Beam 3 90 Ice Fraction, min, all Beams 91 Ice Fraction, min, Beam 1 Ascending 92 Ice Fraction, min, Beam 2 Ascending 93 Ice Fraction, min, Beam 3 Ascending 94 Ice Fraction, min, all Beams Ascending 95 Ice Fraction, min, Beam 1 Descending 96 Ice Fraction, min, Beam 2 Descending 97 Ice Fraction, min, Beam 3 Descending 98 Ice Fraction, min, all Beams Descending Land Contamination 99 Land Fraction, mean, Beam 1 100 Land Fraction, mean, Beam 2 101 Land Fraction, mean, Beam 3 102 Land Fraction, mean, all Beams 103 Land Fraction, mean, Beam 1 Ascending 104 Land Fraction, mean, Beam 2 Ascending 105 Land Fraction, mean, Beam 3 Ascending 106 Land Fraction, mean, all Beams Ascending 107 Land Fraction, mean, Beam 1 Descending 108 Land Fraction, mean, Beam 2 Descending 109 Land Fraction, mean, Beam 3 Descending 110 Ice Fraction, mean, all Beams Descending 111 Land Fraction, max, Beam 1 112 Land Fraction, max, Beam 2 113 Land Fraction, max, Beam 3 114 Land Fraction, max, all Beams 115 Land Fraction, max, Beam 1 Ascending 116 Land Fraction, max, Beam 2 Ascending 117 Land Fraction, max, Beam 3 Ascending 118 Land Fraction, max, all Beams Ascending 119 Land Fraction, max, Beam 1 Descending 120 Land Fraction, max, Beam 2 Descending 121 Land Fraction, max, Beam 3 Descending 122 Land Fraction, max, all Beams Descending 123 Land Fraction, min, Beam 1 124 Land Fraction, min, Beam 2 125 Land Fraction, min, Beam 3 126 Land Fraction, min, all Beams 127 Land Fraction, min, Beam 1 Ascending 128 Land Fraction, min, Beam 2 Ascending 129 Land Fraction, min, Beam 3 Ascending 130 Land Fraction, min, all Beams Ascending 131 Land Fraction, min, Beam 1 Descending 132 Land Fraction, min, Beam 2 Descending 133 Land Fraction, min, Beam 3 Descending 134 Land Fraction, min, all Beams Descending Page History 2016-12-15 -- First version. 2018-09-25 -- Updated Aquarius data to V5.0 (from V4.0). Substantial improvements are provided in the latest version, in particular regarding Aquairus SSS biases at high latitudes and their seasonal variability. References Boutin, J. et al. (2016), Satellite and In Situ Salinity: Understanding Near-Surface Stratification and Subfootprint Variability, Bull. Am. Meteorol. Soc., 97(8), 1391–1407, doi:10.1175/BAMS-D-15-00032.1. Drucker, R., and S. C. Riser (2014), Validation of Aquarius sea surface salinity with Argo: Analysis of error due to depth of measurement and vertical salinity stratification, J. Geophys. Res. Ocean., 119(7), 4626–4637, doi:10.1002/2014JC010045. Lagerloef, G. et al. (2008), The Aquarius/SAC-D Mission: Designed to Meet the Salinity Remote-Sensing Challenge, Oceanography, 21(1), 68–81, doi:10.5670/oceanog.2008.68. Le Vine, D. M., E. P. Dinnat, T. Meissner, S. H. Yueh, F. J. Wentz, S. E. Torrusio, and G. Lagerloef (2015), Status of Aquarius/SAC-D and Aquarius Salinity Retrievals, IEEE J. Sel. Top. Appl. Earth Obs. Remote Sens., 8(12), 5401–5415, doi:10.1109/JSTARS.2015.2427159. Sea-Bird Electronics, Inc., APPLICATION NOTE NO. 69, URL, July 2002.
