Obtaining accurate measurements of the sea surface height from a GPS buoy

A dedicated GPS buoy is designed for calibration and validation(Cal/Val)of satellite altimeters since 2014.In order to evaluate the accuracy of the sea surface height(SSH)measured by the GPS buoy,twelve campaigns have been done within China sea area between 2014 and 2021.In six of these campaigns,two static Global Navigation Satellite System stations were installed at distances of<1 km and 19 km from the buoy to assess how the baseline length influenced the derived SSH from the buoy solutions.The GPS buoy data was processed using the GAMIT/GLOBK software+TRACK module and CSRS-PPP tool to achieve the SSH.The SSH was compared with conventionally tide gauge(TG)data to evaluate the accuracy of the buoy with the standard deviation of the height element.The results showed that the difference in the standard deviation of the SSH from the buoy and the TG was less than 16 mm.The SSHs processed with different ephemeris(Ultra-Rapid,Rapid,Final)were not significantly different.When the baseline length was 19 km,the SSH solution of the GPS buoy performed well,with standard bias of less than 26 mm between the heights measured by the buoy and TG,meaning that the buoy could be used for Cal/Val of altimeters.The bias between the Canadian Spatial Reference System-precise point positioning tool and the TRACK varied a lot,and some of them were over 130 mm.This deemed too high to be useful for Cal/Val of satellite altimeters.Moreover,the GPS buoy solutions processed by GAMIT/GLOBK software+TRACK module were used for in-orbit Cal/Val of HY-2B/C satellites in ten campaigns.The SSH and significant wave height of the altimeters showed good agreements with the GPS buoy solutions.

仿生矿化法制备双磷酸根改性的纤维素/羟基磷灰石复合支架

通过高碘酸钠的氧化以及基于席夫碱原理的阿仑膦酸缩合对支架表面进行功能化改性,最后通过仿生矿化的方式制备了一种新型的双磷酸根纤维素/羟基磷灰石三维复合支架。通过红外光谱仪、扫描电子显微镜、X射线衍射仪、X射线光电子能谱仪对磷酸化改性前后支架的矿化样品的组成、结构和形貌进行分析,结果表明改性后的凝胶支架表面沉积羟基磷灰石的含量、结晶度、晶粒尺寸、Ca/P元素比等,都更接近于天然骨骼中生物磷灰石晶体。细胞增殖毒性检测(CCK-8法)结果揭示了材料无细胞毒性,对矿化样品表面细胞的形貌分析表明,与未改性支架相比,细胞在复合支架上具有更高的活性以及更好的黏附性。因而,改性后的复合支架有望成为一种理想的支架材料。

Preliminary calibration results of the HY-2B altimeter’s SSH at China’s Wanshan calibration site

Satellite altimeter needs to be calibrated to evaluate the accuracy of sea surface height data.The dedicated altimeter calibration field needs to establish a special calibration strategy and needs to evaluate its calibration ability.This paper describes absolute calibration of HY-2 B altimeter SSH using the GPS calibration method at the newly Wanshan calibration site,located in the Wanshan Islands,China.There are two HY-2 B altimeter passes across the Wanshan calibration site.Pass No.362 is descending and the ground track passes the east of Dan’gan Island.Pass No.375 is ascending and crosses the Zhiwan Island.The GPS data processing strategy of Wanshan calibration site was established and the accuracy of GPS calibration method of Wanshan calibration site was evaluated.Meanwhile,the processing strategies of the HY-2 B altimeter for the Wanshan calibration site were established,and a dedicated geoid model data were used to benefit the calibration accuracy.The time-averaged HY-2 B altimeter bias was approximately 2.12 cm with a standard deviation of 2.08 cm.The performance of the HY-2 B correction microwave radiometer was also evaluated in terms of the wet troposphere path delay and showed a mean difference-0.2 cm with a 1.4 cm standard deviation with respect to the in situ GPS radiosonde.

Preliminary calibration results for Jason-3 and Sentinel-3 altimeters in the Wanshan Islands

We present preliminary calibration results for Jason-3 and Sentinel-3A altimeters that we set up in the Wanshan Islands in Guandong Province,China.Two campaigns were carried out in 2018,from March 8 to April 16 and from November 3 to December 11,2018.Three GPS reference stations and tide gauges were established on the islands of Zhiwan,Dangan,and Wailingding during the campaigns.The in-situ sea surface height(SSH)of the altimeter footprint was determined using the tide gauge.The tidal and geoid connection between the tide gauge locations and the altimeter footprints were computed with the NAO.99Jb tidal prediction system and the EGM 2008 geoid,respectively.The data of the tide gauges were defi ned using the GPS buoy and GPS reference stations during the campaigns.The results show that the waveform of the altimeters was slightly contaminated by the small islands.The bias associated with Jason-3 and Sentinel-3A amounted to approximately+20.7±49.7 mm and+30.1±39.4 mm,respectively,which agreed well with the results from other in-situ calibration fi elds.This indicates that the Wanshan area was very suitable as an in-situ calibration/validation fi eld.The wet zenith delay(WZD)determined from the Microwave Radiometer(MWR)and the GPS measurements diff ered from each other for the Jason-3 and Sentinel-3A by−6.6±7.4 mm and 0±6.8 mm,respectively.

Measurement of the sea surface using a GPS towing-body in Wanshan area

Wanshan area has been chosen to be the specified field to calibrate and validate(Cal/Val)the HY-2 altimeter and its follow-on satellites.In March 2018,an experiment has been conducted to determine the sea surface height(SSH)under the HY-2 A ground track(Pass No.203).A GPS towing-body(GPS-TB)was designed to measure the SSH covering an area of about 6 km×28 km wide centered on the HY-2 A altimeter satellite ground track.Three GPS reference stations,one tide gauge and a GPS buoy were placed in the research area,in order to process and resolve the kinematic solution and check the precision of the GPS-TB respectively.All the GPS data were calculated by the GAMIT/GLOBK software and TRACK module.The sea surface was determined by the GPS-TB solution and the tide gauge placed on Zhiwan Island.Then the sea surface of this area was interpolated by Arc GIS10.2 with ordinary Kriging method.The results showed that the precision of the GPS-TB is about 1.10 cm compared with the tide gauge placed nearby,which has an equivalent precision with the GPS buoy.The interpolated sea surface has a bias of–1.5–4.0 cm with standard deviation of 0.2–2.4 cm compared with the checking line.The gradient of the measured sea surface is about 1.62 cm/km along the HY-2 orbit which shows a good agreement compared with the CLS11 mean sea surface(MSS).In the Cal/Val of satellites,the sea surface between the tide gauge/GPS buoy and the footprint of altimeter can be improved by this work.

In situ biosynthesis of bacterial cellulose hydrogel spheroids with tunable dimensions

Bacterial cellulose(BC)hydrogel spheroid plays a significant role in diverse fields due to its spatial 3D structure and properties.In the present work,a series of BC spheroids with controllable size and shape was obtained via an in situ biosynthesis.Crucial factors for fabricating BC spheroid in-cluding inoculum concentration of 1.35×10^(3)CFU/mL,shaking speeds at 100 r/min,and 48-96 h incubation time during the biosynthetic process,were comprehensively established.An operable mechanism model for tuning the size of BC spheroids from 0.4 to 5.0 mm was proposed with a fresh feeding medium strategy of dynamic culture.The resulting BC spheroids exhibit an inter-active 3D network of nanofibers,a crystallinity index of 72.3%,a specific surface area of 91.2 m^(2)/g,and good cytocompatibility.This study reinforces the understanding of BC spheroid forma-tion and explores new horizons for the design of BC spheroids-derived functional matrix materials for medical care.