Validation of Chinese HY-2 satellite radar altimeter significantwave heightYE Xiaomin1, 2, 3, 4, LIN Mingsen3, 4*, XU Ying1, 3, 4

1 College of Information Science and Engineering, Ocean University of China, Qingdao 266100, China2 State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, State Oceanic

Administration, Hangzhou 310012, China3 National Satellite Ocean Application Service, State Oceanic Administration, Beijing 100081, China4 Key Laboratory of Space Ocean Remote Sensing and Application, State Oceanic Administration, Beijing 100081,

China

Received 27 November 2014; accepted 29 January 2015

©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2015

Abstract

Chinese Haiyang-2(HY-2) satellite is the first Chinese marine dynamic environment satellite. The dual-frequency(Ku and C band) radar altimeter onboard HY-2 has been working effective to provide operational significant waveheight (SWH) for more than three years (October 1, 2011 to present).We validated along-track Ku-band SWH dataof HY-2 satellite against National Data Buoy Center (NDBC) in-situ measurements over a time period of threeyears from October 1, 2011 to September 30, 2014, the root mean square error (RMSE) and mean bias of HY-2SWH is 0.38 m and (–0.13±0.35) m, respectively. We also did cross validation against Jason-2 altimeter SWHdata,the RMSE and the mean bias is 0.36m and (–0.22±0.28) m, respectively. In order to compare the statisticalresults between HY-2 and Jason-2 satellite SWH data, we validated the Jason-2 satellite radar altimeter along-trackKu-band SWH data against NDBC measurements using the same method. The results demonstrate the validationmethod in this study is scientific and the RMSE and mean bias of Jason-2 SWH data is 0.26 m and (0.00±0.26) m,respectively. We also validated both HY-2 and Jason-2 SWH data every month, the mean bias of Jason-2 SWH dataalmost equaled to zero all the time, while the mean bias of HY-2 SWH data was no less than –0.31m before April2013 and dropped to zero after that time. These results indicate that the statistical results for HY-2 altimeter SWHare reliable and HY-2 altimeter along-track SWH data were steady and of high quality in the last three years. Theresults also indicate that HY-2 SWH data have greatly been improved and have the same accuracy with Jason-2SWH data after April, 2013. SWH data provided by HY-2 satellite radar altimeter are useful and acceptable forocean operational applications.

Key words: significant wave height, validation, Chinese HY-2 satellite radar altimeter

Citation: Ye Xiaomin, Lin Mingsen, Xu Ying. 2015. Validation of Chinese HY-2 satellite radar altimeter significant wave height. ActaOceanologica Sinica, 34(5): 60–67, doi: 10.1007/s13131-015-0667-y

1  IntroductionSignificant wave height (SWH), defined as the crest-to-trough

height of the 1/3 highest waves in the sea wave field of view, is animportant parameter of ocean research and marine environmentforecast. It is widely used in offshore activities such as transporta-tion, fisheries and oil exploration in ocean. Wave observationsusually come from ships and buoys with the poor data coverage.The satellite radar altimeters, such as Seasat (1978), Geosat(1985−1989), ERS-1 (1991−2000), TOPEX/Poseidon (1992−2006),Geosat Follow-On (1998−2008), ERS-2 (1995−2011), Envisat(2002−2012), Jason-1 (2002−2013) and Jason-2 (2008-present),however, have been providing operational SWH since 1970’s formore than thirty years with global coverage. Chinese Haiyang-2(HY-2) satellite, launched on August 15, 2011, is the firstChinese marine dynamic environment satellite. The radar alti-

meter, operating at 13.58 GHz (Ku band) and 5.25 GHz (C band),onboard HY-2 has been working effective to provide operationalsignificant wave height (SWH) for more than three years (Octo-ber 1, 2011 to present).

The accuracy of altimeter products must be carefully testedbefore being accepted by users (Zhang et al., 2010). Validationactivities, defined as getting the accuracy of the remote sensingproducts by using in-situ data or higher quality remote sensingdata, are necessary not only in estimating the accuracy of the re-mote sensing products, but also in improving the remote sensingextracted algorithm (Chen et al., 1998; Chen, 1999; Chen et al.,1999).

During the development of satellite radar altimeter, lots ofvalidation studies have been done (Queffeulou, 2003; Jiang et al.,2012; Chen et al., 2013; Wang et al., 2013; Xu et al., 2013; Xu et al.,

Acta Oceanol. Sin., 2015, Vol. 34, No. 5, P. 60–67

DOI: 10.1007/s13131-015-0667-y

http://www.hyxb.org.cn

E-mail: hyxbe@263.net

   

Foundation item: The Public Science and Technology Research Funds Projects of Ocean under contract Nos 201105032, 201305032 and201005030; the National High Technology Research and Development Program (863 Program) of China under contract No. 2013AA09A505;Global Change and Air-Sea Interaction Project of China under contract No. GASI-03-03-01-01; the International Science & TechnologyCooperation Program of China under contract No. 2011DFA22260; the Open funds of State Key Laboratory of Satellite Ocean EnvironmentDynamics under contract No. SOED1411.*Corresponding author, E-mail: mslin@mail.nsoas.org.cn

 

 Fig. 1.  Locations and numbers of NDBC buoys and observation stations.

2014; Ye et al., 2014). Korobkin and D’Sa (2008) compared Jason-1 altimeter Ku-band SWH (averaged inside the radius of 10 or 13km) with buoy measurements at National Data Buoy Center(NDBC) stations in the Gulf of Mexico by using a ±30 min time-window, with root-mean-square-error (RMSE) differences of0.17−0.30 m. Durrant et al. (2009) validated Jason-1 (3 452 colloc-ations for 4 years) and ENVISAT (2 157 collocations for 3 years)SWH data with the RMSE of 0.22 m and 0.219–0.202 m by using50-km spatial and 30-minute time window colocation method.Cotton and Carter (1994) and Cheng et al. (2008) comparedmonthly averages of T/P and Jason-2 altimeter SWH data over 2°by 2° areas around the buoys with monthly averages of buoymeasurements with the RMSE of 0.21 m. Wang et al. (2013) valid-ated the HY-2 satellite altimeter along-track Ku band SWH data,902 collocations over the time period from October 1, 2010 to Au-gust 29, 2012, against 60 NDBC buoys with the RMSE of 0.297 m.Xu et al. (2014) also validated HY-2 satellite altimeter SWH data,over the period from October 1, 2010 to June 30, 2012, against 20off shore NDBC buoys with the mean bias of (–0.30±0.38) m.Wang et al. (2013) and Xu et al. (2014) both used the collocationcriteria of 50 km and 30 min window. Though the spatial andtime windows may be different in different collocation methods,the validation results will not be influenced (Ye et al., 2014). Inthis study, we will validate the HY-2 satellite altimeter along-trackKu-band SWH data which cover the period of three years (fromOctober 1, 2011 to September 30, 2014) against NDBC in-situmeasurements and Jason-2 altimeter data.

2  Data

2.1  Satellite radar altimeter data

2.1.1 HY-2 satellite radar altimeterChinese HY-2 satellite, the first Chinese marine dynamic en-

vironment satellite, was launched at 22:57 UTC, on August 15,2011. The payloads of HY-2 satellite include a dual-frequencyradar altimeter operating at 13.58 GHz (Ku band) and 5.25 GHz(C band), DORIS,a microwave scatterometer, a scanning mi-crowave radiometer and a calibration microwave radiometer.The orbit of HY-2 satellite is sun-synchronous with a 14-day cyclein the first half of its lifetime at an altitude of 971 km, while thelast half of lifetime at an altitude 973 km with a 168-day cycle. Theobjective of HY-2 is monitoring the dynamic ocean environmentby using microwave sensors onboard. It is used to detect globalsea surface wind field, sea surface height, significant wave heightand sea surface temperature in all-weather.

National Satellite Ocean Application Service (NSOAS), StatesOceanic Administration (SOA) of China offers the HY-2 satellitedata to public for free. The along-track HY-2 satellite radar alti-meter SWH data used in this paper are downloaded from NSOAS(http://www.nsoas.org.cn/NSOAS_En/index.html).

2.1.2  Jason-2 satellite radar altimeterOcean Surface Topography Mission (OSTM) /Jason-2 satel-

lite was launched by NASA (United Sates of America) and FrenchSpace Agency on June 20, 2008. Onboard the Jason-2 satellite, thepayload is composed of Poseidon-3 radar altimeter supplied byNational Centre for Space Studies (CNES, French: Center of Na-tional D’ études spatiales), an Advanced Microwave Radiometersupplied by NASA/JPL. It is a continuation to the TOPEX/Pos-eidon and Jason-1 altimetry missions developed by CNES andNASA. The Jason-2 radar altimeter also works on dual-frequencyat 13.575 GHz (Ku band) and 5.3 GHz (C band). Jason-2 satelliteis placed in the same orbit as its predecessor Jason-1 and T/P, in-clined 66° and at an altitude of 1 336 km, with a 9.915-day repeatcycle. It provides ocean surface topography, surface wind speed,significant wave height together in high accuracy.

The Jason-2 altimetry Geophysical Data Record (GDR) datahave 254 passes in each cycle with 127 ascending passes and 127descending passes, respectively. The along-track Jason-2 SWHdata used in this paper are downloaded from AVISO/CNES(http://www.aviso.altimetry.fr/en/data.html).

All the along-track SWH data in this study are Ku-band SWHof satellite radar altimeter. Data edits are necessary before valida-tion. We delete the SWH data with land, ice and rain index, andmake sure the SWH data are in the range of 0 to 11 m with thebackscatter coefficients no larger than 35 dB.

2.2  National Data Buoy Center (NDBC) SWH dataThe in-situ SWH, measured by moor buoys or observation

stations, used in this study are obtained from National Oceanicand Atmospheric Administration’s (NOAA) National Data BuoyCenter (NDBC). The data are downloaded from http://www.nd-bc.noaa.gov/.

Every NDBC SWH is calculated as the average of the highestone-third of all of the wave heights during the 20-min samplingperiod. The NDBC SWH measurements reported once per hour,together with the measured time in UTC and unit in meter. Thetotal 71 measured buoys and observation stations, both for HY-2and Jason-2 altimeter SWH data comparing, are located in thecoastline of Northern America, Gulf of Mexico and east-northernof Pacific Ocean as show in Fig. 1.

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3  Validation methodsTo obtain a set of simultaneous SWH data from satellite radar

altimeter and in-situ measurements at each buoys or observa-tion sites for validation comparing. Many collocation proceduremethods are used in altimeter validation studies (Cotton andCarter, 1994; Korobkin and D’Sa, 2008; Cheng et al., 2008; Dur-rantet al., 2009; Ye et al., 2014). Usually, the satellite altimeterdata points in the closest path which are within a certain radiusform the observation site, a 50-km radius is widely used in alti-meter SWH validation studies, are averaged as the satellite alti-meter data value, as show in Fig. 2. These averaged altimeter datamust be quality controlled by removing individual observationsgreater or less than 3 standard deviations away from the mean forthese data. In additional, the mean value with the number of theaveraged altimeter data points is less than 6 will be deleted forvalidation. Hourly buoy SWH data were then linearly interpol-ated to the altimeter overpass time, with the additional criterionthat there is at least one buoy observation within 0.5 h before or0.5 h after the time of the altimeter overpass (i.e., within a 30-mintime window). In other words, the hourly buoy SWH data used tocollocate must be available. This interpolated buoy data and themean of the quality controlled altimeter observations made up asingle collocation (Durrantet al., 2009).

 

 Fig. 2.  Schematic case of collocation between satellite alti-meter observation and in-situ measurement. The blackstar point is the location of NDBC station with the ID of41049, solid dots (both red and blue) are altimeter obser-vations of HY-2 with the pass number of 314; red solid dotsare the altimeter observation points used to be averaged.

 For the cross validation of satellite altimeter SWH data, a two-

step collocation method will be used. Firstly, the crossover pointsof the ground-track between the two altimeter paths should befound. The time difference between the two altimeters measure-mentson crossover points is less than one hour are selected forcross comparisons. Secondly, in order to filter time and spacevariability effects of altimeter consecutive measurements on itspass, one second elementary altimeter measurements over 50 kmalong-track, 25 km each side of the crossover point, the number

of which is larger than or equal to 6 for both HY-2 and Jason-2,are averaged as the comparison (Cotton and Carter, 1994).

The statistics for satellite radar altimeter SWH data validationused in this study are linear correlation coefficient (R), mean bi-as (Bias), standard deviations of bias (STD) and root-mean-square-error (RMSE), defined as follows:

R =

NPi=1

(X i ¡ ¹X )(Yi ¡ ¹Y)sNP

i=1

(X i ¡ ¹X )2NP

i=1

(Yi ¡ ¹Y)2

; (1)

B ias =NX

i=1

(X i ¡ Yi)=N; (2)

STD =

vuuut NPi=1

(X i ¡ Yi ¡ X ¡ Y)2

N ¡ 1;

(3)

R MSE =

vuuut NPi=1

(X i ¡ Yi)2

N:

(4)

X i

Yi

where N is the number of collocations, is the value of alti-meter data validated, and is the value of in-situ data or highquality altimeter data used as true value. R is a measure of thestrength and direction of the linear relationship between twovariables. Bias is the mean value of differences between two vari-ables. STD measures the amount of variation or dispersion fromthe average. A low STD indicates that the data points tend to bevery close to the mean; a high STD indicates that the data pointsare spread out over a large range of values. RMSE is a measure ofprecision of the data. All of above four indices can characterizethe error property of altimeter SWH data together.

4  Results and discussion

4.1  Validation results of HY-2 SWH against NDBCin-situ meas-urementsStatistical results of HY-2 altimeter SWH validated against

NDBCin-situ measurements in deferent time span are given inTable 1. In order to compare the statistical results between HY-2and Jason-2 satellite, we also validated Jason-2 altimeter SWHdata using the same method, the same study region and buoydata as show in Fig. 1. The validation results of Jason-2 altimeterSWH against NDBC SWH are also listed in Table 1.

3 745 collocation SWH data points are used to calculate thestatistics with the mean bias and RMSE of HY-2 altimeter SWHbeing (–0.13±0.35) m and 0.38 m respectively over the period of 3years (from October 1, 2011 to September 30, 2014). The correla-tion between HY-2 altimeter SWH and NDBC in-situ measure-ments is high with the linear correlation coefficient of 0.95. Themean bias, RMSE and linear correlation coefficient of validatingJason-2 SWH against NDBC are (0.00±0.26) m, 0.26 m and 0.97m, respectively, which are the same with other studies (Abdalla etal., 2008; Dumont et al., 2008). There are no significantly differ-ences of validation statistics indices between HY-2 and Jason-2SWH data. This result indicates that HY-2 SWH data are of highquality. The scatter plot comparisons are shown in Fig. 4.

We redo the validation by using along-track SWH data meas-ured in every month to get a time series of monthly mean bias ofaltimeter SWH data. The validation results are different in differ-ent time, as show in Table 1 and Fig. 5.

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 Fig. 3.  Schematic case of cross collocation between HY-2 (blue line and points) and Jason-2 (red line and points) satellite. The red(blue) solid dots insidethe circle with a radius of 25 km are averaged as the collocation value.

Table 1.  Validation results of HY-2 and Jason-2 satellite radar altimeters significant wave height against NDBC buoys measurements

Time spanHY-2   Jason-2

N R Bias/m STD/m RMSE/m   N R Bias/m STD/m RMSE/m

10/20111)−12/2013 3 745 0.95 –0.13 0.35 0.38   4 528 0.97 0.00 0.26 0.26

10/2011 90 0.96 –0.31 0.35 0.47   161 0.98 –0.03 0.23 0.23

11/2011 133 0.97 –0.25 0.34 0.43   149 0.99 –0.06 0.22 0.23

12/2011 121 0.97 –0.21 0.32 0.38   164 0.99 –0.03 0.22 0.22

1/2012 127 0.98 –0.28 0.30 0.40   160 0.98 –0.03 0.26 0.26

2/2012 131 0.96 –0.23 0.37 0.44   138 0.98 –0.06 0.28 0.29

3/2012 121 0.97 –0.30 0.31 0.43   143 0.98 –0.02 0.27 0.27

4/2012 115 0.94 –0.18 0.34 0.39   143 0.96 0.00 0.26 0.26

5/2012 107 0.95 –0.22 0.29 0.36   140 0.97 –0.02 0.22 0.22

6/2012 98 0.87 –0.17 0.35 0.39   132 0.94 –0.01 0.22 0.22

7/2012 89 0.88 –0.22 0.26 0.34   126 0.91 0.02 0.25 0.25

8/2012 135 0.76 –0.06 0.37 0.37   124 0.85 0.06 0.30 0.30

9/2012 99 0.94 –0.15 0.27 0.31   121 0.98 0.03 0.18 0.18

10/2012 114 0.92 –0.20 0.47 0.51   126 0.98 0.04 0.27 0.27

11/2012 143 0.97 –0.25 0.36 0.43   125 0.97 0.00 0.26 0.25

12/2012 104 0.96 –0.26 0.44 0.51   124 0.97 –0.04 0.29 0.30

1/2013 100 0.80 –0.19 0.58 0.60   123 0.97 0.01 0.26 0.26

2/2013 88 0.97 –0.30 0.39 0.48   97 0.98 –0.01 0.22 0.22

3/2013 88 0.97 –0.19 0.26 0.32   102 0.94 0.01 0.33 0.33

4/2013 28 0.93 0.02 0.31 0.30   94 0.97 0.02 0.20 0.20

5/2013 101 0.96 –0.06 0.22 0.23   115 0.95 0.04 0.21 0.21

6/2013 82 0.91 –0.01 0.29 0.29   102 0.94 0.06 0.22 0.23

7/2013 92 0.72 0.02 0.37 0.37   102 0.94 0.05 0.19 0.19

8/2013 71 0.77 0.03 0.32 0.32   105 0.93 0.07 0.23 0.23

9/2013 92 0.94 –0.02 0.39 0.38   93 0.98 0.01 0.30 0.30

10/2013 99 0.96 0.01 0.33 0.33   114 0.98 –0.01 0.26 0.26

11/2013 103 0.98 –0.09 0.21 0.22   117 0.97 –0.05 0.31 0.31

12/2013 107 0.96 –0.03 0.31 0.31   118 0.98 0.01 0.20 0.20

1/2014 115 0.96 0.00 0.31 0.31   110 0.97 –0.01 0.32 0.32

2/2014 88 0.97 –0.08 0.25 0.26   93 0.96 0.02 0.29 0.29

3/2014 96 0.97 –0.05 0.25 0.25   96 0.96 –0.05 0.36 0.36

4/2014 98 0.91 –0.05 0.33 0.33   106 0.98 –0.04 0.21 0.22

5/2014 65 0.91 –0.03 0.21 0.21   115 0.86 0.07 0.31 0.32

6/2014 84 0.86 0.02 0.35 0.35   106 0.92 0.06 0.30 0.30

7/2014 97 0.77 0.02 0.38 0.37   124 0.89 0.06 0.22 0.23

8/2014 102 0.85 –0.02 0.26 0.26   140 0.94 0.03 0.25 0.25

9/2014 91 0.91 –0.04 0.34 0.34   133 0.96 0.01 0.24 0.24

Notes: 1)10/2011 meansthe time span of October, 2011. The follows are the same.

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 Fig. 4.  Scatter plot comparisons of significant wave height between satellite altimeter (a. HY-2, b. Jason-2) and NDBCmeasurements over the period from October 1, 2011 to September 30, 2014. The blue line in the figure is the best fitting lineof thecomparing SWH data points; the red line is the contour line of them.

 

 Fig. 5.  Time series of monthly mean Bias (a) and RMSE (b) of significant wave height of HY-2 and Jason-2 altimeter validatedagainst NDBC in-situ measurements from October 2011 to September 2014. The performance of SWH detection of HY-2 satelliteisdivided to 3 phases. Phase 1 (October 2011–September 2012): steady and relative high quality; Phase 2 (October 2012–March 2013):relative low quality; Phase 3 (April 2013–September 2014): excellent, as good as Jason-2.

64 YE Xiaomin et al. Acta Oceanol. Sin., 2015, Vol. 34, No. 5, P. 60–67  

 

 Fig. 6.  Locations of crossover points of HY-2 and Jason-2 satellite ground-tracks.

 

It is apparent from Fig. 5 that Jason-2 has high and steadyquality SWH data with the RMSE from 0.2 m to 0.3 m and the bi-as nearly equal to zero meters (comparing against to NDBCin-situ measurements). The performance of SWH detection of HY-2is divided to 3 phases, as show in Fig. 5. HY-2 SWH data are alsosteady and of relative high quality except during period from Oc-tober 2012 to March 2013. The RMSE of HY-2 SWH data are vari-able from 0.31 m to 0.47 m during period from October 2011 toSeptember 2012 (Phase 1). After a one-year consecutive opera-tion, The RMSE of HY-2 SWH data increase to larger than thethreshold of 0.5 m during period from October 2012 to March2013 (Phase 2). Then the statistics results, including bias andRMSE, have reached to the level of Jason-2 since April 2013 withthe RMSE of no more than 0.4 m and the bias close to zero (from–0.08 to 0.02). The validation results are also listed in Table 1.

The RMSE of HY-2 SWH data validated against NDBC buoymeasurements varies from 0.34 m to 0.44m in the time periodfrom October, 2011 to August, 2012, and the STD is less than 0.37m in the period from October, 2011 to June, 2012, as listed in Ta-ble 1 and Fig. 5. Wang et al. (2013) and Xu et al. (2014) also valid-ated the HY-2 altimeter SWH data against NDBC measurements,respectively. The RMSE of 0.297 m in Wang et al. (2013) and theSTD of 0.38 m in Xu et al. (2014) are both different from this

study. The reason is that different buoys were selected in valida-tion. For example, 60 buoys with 902 collocations were used inWang et al. (2013) and 71 buoys with 1 267 collocations wereused in this study in the period from October, 2011 to August,2012. The quality of HY-2 altimeter SWH data dropped in Phase 2(time period from October 2012 to March 2013) may be causedby the sensor. Electronics drift and sensor degradations can af-fect the quality of measurements (Queffeulou, 2003).There maybe two causes for that the mean bias of HY-2 altimeter SWH dataagainst buoys measurements dropped from 0.3 m to almost zeroin April, 2013. The first one is that the data processing algorithmhas been improved. Another is that the backup radar altimeteronboard HY-2 satellite has been working since that time. Thereisn’t any official announce appeared for these reasons, so the realcauses should be confirmed in the future.

4.2  Cross validation results of HY-2 SWH against Jason-2We also do the cross validation of HY-2 altimeter along-track

Ku-band SWH against Jason-2 data by using the method men-tioned in Section 3. We get 14 570 cross validation collocations intotal over period from October 1, 2011 to September 30, 2014 withthe crossover points of the two satellite ground- tracks in globalocean, as show in Fig. 6.

The cross validation results are show in Table 2, Figs 7 and 8.The mean bias and RMSE of HY-2 SWH data is (–0.22±0.28) mand 0.36 m compared with Jason-2 by using the data over theperiod from October 1, 2011 to September 30, 2014, respectively.The linear correlation coefficient between HY-2 altimeter SWHand Jason-2 SWH is 0.98.

The time series of cross validation results are show in Fig. 8. Italso shows that the HY-2 SWH data are stable and of high qualityduring its consecutive operation period from October 1, 2011 topresent. The bias dropped towards to zero in April 2013, which isthe same conclusion as the validation results compared with ND-BC buoys data. The R, Bias, STD and RMSE of cross validation arenot equal to that validated against buoy measurements. The dif-

ferent locations of collocations and study region (as shown inFigs 1 and 6) lead to the different validation results. So the resultsfor two validation activities are both reliable, they show the qual-ity of HY-2 altimeter SWH data compared to different data in dif-ferent region.

5  ConclusionsIn this study, we validated the Ku-band SWH data of HY-2

satellite radar altimeter against NDBC in-situ measurements andJason-2 satellite altimeter over the time period from October 1,2011 to September 30, 2014 by using altimeter observation datacollocation methods. The validation results are summarized asfollow.

  YE Xiaomin et al. Acta Oceanol. Sin., 2015, Vol. 34, No. 5, P. 60–67 65

 

 Fig. 8.  Time series of Bias and RMSE of significant wave height of HY-2 altimeter cross validated against Jason-2 altimetermeasurements every month.

Table 2.  Cross validation results of HY-2 altimeter significantwave height against Jason-2

Time span   N R Bias/m STD/m RMSE/m10/2011−9/2014   14 570 0.98 –0.22 0.28 0.36

10/2011   208 0.99 –0.37 0.29 0.4711/2011   293 0.99 –0.32 0.22 0.3912/2011   495 0.98 –0.29 0.20 0.351/2012   341 0.98 –0.31 0.27 0.422/2012   322 0.99 –0.30 0.15 0.343/2012   436 0.99 –0.32 0.23 0.394/2012   523 0.99 –0.32 0.22 0.385/2012   278 0.98 –0.33 0.28 0.436/2012   226 0.98 –0.32 0.28 0.427/2012   428 0.99 –0.31 0.29 0.438/2012   571 0.98 –0.27 0.32 0.429/2012   206 0.98 –0.31 0.35 0.47

10/2012   207 0.96 –0.26 0.39 0.4711/2012   514 0.98 –0.30 0.25 0.3912/2012   448 0.99 –0.31 0.20 0.371/2013   324 0.97 –0.30 0.30 0.432/2013   365 0.98 –0.31 0.25 0.403/2013   438 0.99 –0.31 0.19 0.364/2013   106 0.98 –0.17 0.27 0.325/2013   330 0.98 –0.18 0.31 0.366/2013   216 0.95 –0.14 0.46 0.487/2013   511 0.99 –0.14 0.21 0.268/2013   258 0.97 –0.14 0.42 0.449/2013   247 0.97 –0.14 0.31 0.34

10/2013   279 0.97 –0.09 0.34 0.3511/2013   578 0.99 –0.13 0.16 0.2112/2013   276 0.97 –0.14 0.33 0.361/2014   842 0.99 –0.15 0.20 0.252/2014   772 0.99 –0.18 0.22 0.283/2014   1 084 0.98 –0.12 0.24 0.27

4/2014   485 0.98 –0.15 0.24 0.285/2014   252 0.97 –0.11 0.32 0.346/2014   336 0.97 –0.12 0.38 0.407/2014   523 0.98 –0.12 0.29 0.328/2014   174 0.96 –0.11 0.34 0.369/2014   196 0.98 –0.12 0.35 0.37 

 Fig. 7.  Scatter plot comparisons of significant wave heightbetween HY-2 and Jason-2 satellite altimeter during peri-od from October 1, 2011 to September 30, 2014. The blueline in the figure is the best fitting line of the comparingSWH data points; the red line is the contour line of them.

 

(1) Comparison with NDBC observation measurements, The

HY-2 satellite altimeter along-track Ku-band SWH data are stable

and of high quality with the mean bias, RMSE and linear correla-

tion coefficient of (–0.13±0.35) m, 0.38 m and 0.95, respectively.

(2) Comparison with Jason-2 observation measurements, The

HY-2 satellite altimeter SWH data are also stable and of high

quality with the mean bias, RMSE and linear correlation coeffi-

cient of (–0.22±0.28) m, 0.36 m and 0.98, respectively.

(3) HY-2 satellite radar altimeter has been working well in

SWH observation as Jason-2 since April 2013 with the bias of

nearly to zero.

66 YE Xiaomin et al. Acta Oceanol. Sin., 2015, Vol. 34, No. 5, P. 60–67  

Acknowledgements

The Jason-2 SWH data are downloaded from AVISO/CNES

(http://www.aviso.altimetry.fr/en/data.html). The NDBC buoys

data are downloaded from NDBC/NOAA (http://www.ndbc.

noaa.gov/). We thank these organizations offering the data.

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