scholarly journals ICESat-derived inland water surface spot heights

2016 ◽  
Vol 52 (4) ◽  
pp. 3276-3284 ◽  
Author(s):  
Fiachra E. O'Loughlin ◽  
Jeffrey Neal ◽  
Dai Yamazaki ◽  
Paul D. Bates
Keyword(s):  
Water Surface ◽  
Inland Water ◽  
Surface Spot

Evaluation of Sentinel-3 SRAL SAR Altimetry over Recently Constructed Global Reservoirs

2020 ◽  
Author(s):  
Xingxing Zhang ◽  
Liguang jiang ◽  
Zhijun Yao ◽  
Zhaofei Liu ◽  
Rui Wang ◽  
...  
Keyword(s):  
Water Surface ◽  
Tracking System ◽  
A Priori ◽  
Open Loop ◽  
Water Bodies ◽  
Surface Elevation ◽  
Radar Altimetry ◽  
Inland Water ◽  
Water Surface Elevation ◽  
Inland Water Bodies

<p>Satellite radar altimetry is increasingly being used for hydrological studies. However, it is still challenging to deliver high quality data over inland water bodies, i.e. lakes, rivers and reservoirs. One of the reasons is that the positioning of the range window is difficult due to highly variable topography and water surface elevation. To address this issue, Sentinel-3, the first SAR altimeter operating at global scale, is configured with a new on-board tracking system, i.e. open-loop mode. An open-loop tracking system can position the range window very efficiently based on a priori surface elevation stored on-board. In this context, a suitable a priori surface elevation of inland water bodies is very important.</p><p>Sentinel-3 is operating based on a pseudo-DEM controlled through the Open-Loop Tracking Command (OLTC). <strong> </strong>The current OLTC V5 (operated after March 2019) is generated based on an inland water mask and Altimeter corrected Elevations (ACE-2), which is created using multi-mission Satellite Radar Altimetry from 1994-2005 in combination with the Shuttle Radar Topography Mission (SRTM). However, OLTC V5 still misses some inland water bodies and contains some incorrect surface elevations, especially over newly built reservoirs, where the difference between water surface elevation and ACE-2 can exceed 100m.</p><p>In this study, a comprehensive evaluation of Sentinel-3A (S3A) is conducted at 26 globally-distributed recently constructed large reservoirs. The results show that S3A fails to deliver useful data over most new reservoirs in open loop due to the incorrect a priori elevations stored in OLTC V5. On the contrary, S3A closed-loop (operated before March 2019) can deliver useful data in many cases.</p><p>To improve the OLTC table, we propose two approaches. The first one is to use dam height to correct the a priori surface elevation, which is relevant for very recently completed dams or dams under construction. The other is to use water surface elevation from Cryosat-2 to update the OLTC table. The approaches are demonstrated for reservoirs located on the Lancang and Nu rivers in the Southwest of China. The updated OLTC table will help exploit the Sentinel-3 radar altimetry mission to its full potential, enabling it to correctly track water surface elevation in a larger number of water bodies.</p>

Long-term changes in inland water surface temperature across China based on remote sensing data

2020 ◽  
Author(s):  
Rui Wang ◽  
Xin Yan ◽  
Zhenguo Niu ◽  
Wei Chen
Keyword(s):  
Climate Change ◽  
Surface Water ◽  
Surface Temperature ◽  
Water Surface ◽  
Annual Variation ◽  
Average Rate ◽  
Transform Method ◽  
Inland Water ◽  
The Past ◽  
Water Surface Temperature

AbstractWater surface temperature is a direct indication of climate change. However, it is not clear how have China’s inland waters responded to climate change in the past using a consistent method on a national scale. In this study, we used Moderate Resolution Imaging Spectroradiometer (MODIS) data from 2000 to 2015 to study the temporal and spatial variation characteristics of water surface temperature in China using the wavelet transform method. The results showed the following: (1) the freezing date of China inland water has shown a significant delaying trend during the past 16 years with an average rate of -1.5 d/a; (2) the shift of 0°C isotherm position of surface water across China has clear seasonal changes, which first moved eastward about 25° and northward about 15°, and then gradually moved back after the year 2009; (3) during the past 16 years, 0°C isotherm of China’s surface water has gradually moved north by about 0.09° in the latitude direction and east by about 1° in the longitude direction; (4) the inter-annual variation of water surface temperature in 17 lakes of China showed a similar fluctuation trend that increased before 2010, and then decreased. The El Niño and La Niña around 2010 could have impacts on the turning point of the annual variation of water surface temperature. This study validated the response of China’s inland surface water to global climate change and improved the understanding of the wetland environment’s response to climate change.

scholarly journals S3MPC: Improvement on Inland Water Tracking and Water Level Monitoring from the OLTC Onboard Sentinel-3 Altimeters

2020 ◽  
Vol 12 (18) ◽  
pp. 3055
Author(s):  
Nicolas Taburet ◽  
Lionel Zawadzki ◽  
Maxime Vayre ◽  
Denis Blumstein ◽  
Sophie Le Gac ◽  
...  
Keyword(s):  
Water Level ◽  
Water Surface ◽  
Closed Loop ◽  
Open Loop ◽  
Water Bodies ◽  
Inland Water ◽  
Ice Caps ◽  
Ground Segment ◽  
Tracking Mode ◽  
Product Service

The Sentinel-3A and Sentinel-3B satellites were launched, respectively, on 16 February 2016 and 25 April 2018 as part of the European Copernicus program. The Sentinel-3 Surface Topography Mission makes use of the altimeter instruments onboard Sentinel-3A and Sentinel-3B to provide elevation measurements not only of the ocean water level but also of the inland waters and ice caps. For the first time, the altimeters onboard Sentinel-3A and Sentinel-3B are operated in Synthetic Aperture Radar mode over all Earth surfaces. They also benefit from elevation priors (the Open-Loop Tracking Command) allowing them to precisely position their receiving window to track the backscattered signal from the inland water targets to be monitored rather than relying on the traditional Closed-Loop tracking mode. This paper makes use of the Sentinel-3A/Sentinel-3B tandem phase to assess the benefits of the Open-Loop tracking mode compared to Closed-Loop. Longer time series are also used to highlight the improvements in terms of the percentage of points over which the altimeter hooks on water surfaces and water surface height estimation brought by the switch of Sentinel-3A from the Closed-Loop to Open-Loop tracking mode as well as the successive Open-Loop Tracking Command updates. In particular, it is shown that from a Level-3 water level product service perspective, the increase in the number of water bodies with valid water surface height estimates is of the order of 25% in Open-Loop with respect to Closed-Loop with similar precision. It is also emphasized that the Open-Loop Tracking Command update onboard Sentinel-3A from v. 4.2 to v. 5.0 yielded a 30% increase in the number of water bodies over which valid water surface height could be estimated. Eventually, the importance of knowing whether a water target was associated with a fine-tuned Open-Loop Tracking Command or an interpolated one is stressed and the recommendation to provide such a flag in the Sentinel-3 Level2 Payload Data Ground Segment products is emitted.

scholarly journals Human Activities and Climate Variability Affecting Inland Water Surface Area in a High Latitude River Basin

Water ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 382 ◽  
Author(s):  
Liwen Chen ◽  
Guangxin Zhang ◽  
Y. Jun Xu ◽  
Shengbo Chen ◽  
Yanfeng Wu ◽  
...  
Keyword(s):  
Surface Area ◽  
River Basin ◽  
High Latitude ◽  
Human Activities ◽  
Water Surface ◽  
Water Bodies ◽  
Total Water ◽  
Inland Water ◽  
Water Surface Area ◽  
Inland Water Bodies

Spatiotemporal changes in the surface area of inland water bodies have important implications in regional water resources, flood control, and drought hazard prediction. Although inland water bodies have been investigated intensively, few studies have looked at the effect of human activities and climate variability on surface area of inland waters at a larger scale over time and space. In this study, we used MODIS (MOD13Q1) images to determine water surface area extent at 250 m spatial resolution. We then applied this algorithm with MOD13Q1 images taken at 16-day intervals from 2000 to 2018 to a large river basin in China’s northeast high latitude region with dense stream network and abundant wetlands to investigate spatiotemporal distribution and dynamics of inland water bodies. The study identified 209 ponds, lakes, and reservoirs with an average total surface area of 2080 km2 in the past 19 years. The total water surface area fluctuated largely from 942 km2 to 5169 km2, corresponding to rainfall intensity and flood. We found that the total water surface area in this high latitude river basin showed an increasing trend during the study period, while the annual precipitation amount in the river basin also had an increasing trend concurrently. Precipitation and irrigation significantly contributed to the monthly change of water surface area, which reached the highest during June and August. The increase of water surface area was significant in the lower basin floodplain region, where agricultural irrigation using groundwater for rice production has progressed. Four nationally important wetland preserves (Zhalong, Xianghai, Momoge, and Chagan Lake) in the river basin made up nearly 50% of the basin’s total water surface area, of which Zhalong, Xianghai, and Momoge are designated by The Ramsar Convention as wetland sites of international importance. Seasonally, these water bodies reached their maximal surface area in August, when both the monsoon weather and agricultural discharge prevailed. This study demonstrates that water surface area in a high latitude river basin is affected by both human activities and climate variation, implying that high latitude regions will likely experience more changes in surface water distribution as global climate change continues and agriculture becomes intensified.

Immunoferritin localization of intracellular antigens in positively stained frozen sections

1978 ◽  
Vol 36 (2) ◽  
pp. 168-169
Author(s):  
K. T. Tokuyasu
Keyword(s):  
Surface Tension ◽  
Water Surface ◽  
Thin Layers ◽  
The Other ◽  
Positive Staining ◽  
Frozen Sections ◽  
The Past ◽  
Ultrathin Frozen Sections ◽  
Definition Of

During the past investigations of immunoferritin localization of intracellular antigens in ultrathin frozen sections, we found that the degree of negative staining required to delineate u1trastructural details was often too dense for the recognition of ferritin particles. The quality of positive staining of ultrathin frozen sections, on the other hand, has generally been far inferior to that attainable in conventional plastic embedded sections, particularly in the definition of membranes. As we discussed before, a main cause of this difficulty seemed to be the vulnerability of frozen sections to the damaging effects of air-water surface tension at the time of drying of the sections.Indeed, we found that the quality of positive staining is greatly improved when positively stained frozen sections are protected against the effects of surface tension by embedding them in thin layers of mechanically stable materials at the time of drying (unpublished).

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