Sea Surface Salinity | Validation dataset containing Aquarius SSS and Argo float observations

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:

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 monthly sea surface salinity retrieved by the Aquarius instrument SSS

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 day
25 km

+/- 0.5 day
75 km
+/- 3.5 day
25 km
+/- 3.5 day
75 km
+/- 15 days
25 km
+/- 15 days
75 km
6.3MB  18.8MB  39.5MB  95.5MB 47.9MB   105.0MB

 

 

Spatial distribution collocations sea surface salinity SSS Argo Aquarius

Fig. 1 Positions of individual Argo observations reported in the global dataset during the period Aug 25 2011 – June 07 2015.

 

Number of collocations sea surface salinity SSS Argo Aquarius monthly

Fig. 2 Number of monthly Argo SSS observations versus time reported in the global dataset.

 

Argo sea surface salinity SSS spatial distribution density

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.

 

Histogram of number of Argo sea surface salinity observations  per grid cell

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.

Ocean basin definition World Ocean Atlas 2009

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

http://aquarius.nasa.gov/

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.