Antarctic sea ice is an important part of the Earth’s atmospheric system,and satellite remote sensing is an important technology for observing Antarctic sea ice.Whether Chinese Haiyang-2B(HY-2B)satellite altimeter da...Antarctic sea ice is an important part of the Earth’s atmospheric system,and satellite remote sensing is an important technology for observing Antarctic sea ice.Whether Chinese Haiyang-2B(HY-2B)satellite altimeter data could be used to estimate sea ice freeboard and provide alternative Antarctic sea ice thickness information with a high precision and long time series,as other radar altimetry satellites can,needs further investigation.This paper proposed an algorithm to discriminate leads and then retrieve sea ice freeboard and thickness from HY-2B radar altimeter data.We first collected the Moderate-resolution Imaging Spectroradiometer ice surface temperature(IST)product from the National Aeronautics and Space Administration to extract leads from the Antarctic waters and verified their accuracy through Sentinel-1 Synthetic Aperture Radar images.Second,a surface classification decision tree was generated for HY-2B satellite altimeter measurements of the Antarctic waters to extract leads and calculate local sea surface heights.We then estimated the Antarctic sea ice freeboard and thickness based on local sea surface heights and the static equilibrium equation.Finally,the retrieved HY-2B Antarctic sea ice thickness was compared with the CryoSat-2 sea ice thickness and the Antarctic Sea Ice Processes and Climate(ASPeCt)ship-based observed sea ice thickness.The results indicate that our classification decision tree constructed for HY-2B satellite altimeter measurements was reasonable,and the root mean square error of the obtained sea ice thickness compared to the ship measurements was 0.62 m.The proposed sea ice thickness algorithm for the HY-2B radar satellite fills a gap in this application domain for the HY-series satellites and can be a complement to existing Antarctic sea ice thickness products;this algorithm could provide long-time-series and large-scale sea ice thickness data that contribute to research on global climate change.展开更多
Icebergs are big chunks of ice floating on the ocean surface,and melting of icebergs contributes for the major part of freshwater flux into ocean.Dynamic monitoring of the icebergs in Antarctica and accurate estimatio...Icebergs are big chunks of ice floating on the ocean surface,and melting of icebergs contributes for the major part of freshwater flux into ocean.Dynamic monitoring of the icebergs in Antarctica and accurate estimation of their volume are important for predicting the trend of freshwater budget of the Southern Ocean.The iceberg freeboard is a key parameter for measuring the thickness and volume of an iceberg and is defined as the difference between the elevation of iceberg surface and sea level.So far,freeboards of icebergs have been successfully extracted using InSAR DEM,and the laser and radar altimeter.However,uncertainties exist in these results mainly caused by missed detection of small icebergs due to the spatially sparse and temporally incomplete data coverage.In addition to the above techniques,optical images can also be used to extract the iceberg freeboard based on its geometric relationship with shadow length,which can effectively compensate for the above shortcomings.Although the feasibility has been preliminarily presented,the precision and extensive application of shadow-height method deserves further research,such as estimating the basal melting of icebergs.In this work,we tested an optical image-based freeboard extraction method over icebergs in Prydz Bay,Antarctica.A normalized shadow pixel index(NSPI)is designed to identify iceberg shadows with different shapes in HY-1C/D CZI and Sentinel-2 MSI optical images.The iceberg freeboard can be determined with an acceptable precision(2 m)in optical images compared with laser altimeter(i.e.ICESat-2)measurements.Moreover,basal melting of icebergs has been assessed according to the variation of freeboard using repeated optical observations.The results indicate that icebergs in the study area were with a mean freeboard of about 56 m in early December 2022,and experienced a decrease in freeboard of 1.9 m within two months,in correspondence with the Antarctic seasonal trend.The methodological framework,therefore,turns out to be a reliable complementary approach to studying the iceberg freeboard in polar regions.展开更多
The negative freeboard of sea ice(i.e., the height of ice surface below sea level) with subsequent flooding is widespread in the Southern Ocean, as opposed to the Arctic, due to the relatively thicker ice and thinner ...The negative freeboard of sea ice(i.e., the height of ice surface below sea level) with subsequent flooding is widespread in the Southern Ocean, as opposed to the Arctic, due to the relatively thicker ice and thinner snow. In this study, we used the observations of snow and ice thickness from 103 ice mass balance buoys(IMBs) and NASA Operation IceBridge Aircraft Missions to investigate the spatial distribution of negative freeboard of Arctic sea ice. The Result showed that seven IMBs recorded negative freeboards, which were sporadically located in the seas around Northeast Greenland, the Central Arctic Ocean, and the marginal areas of the Chukchi–Beaufort Sea. The observed maximum values of negative freeboard could reach-0.12 m in the seas around Northeast Greenland. The observations from IceBridge campaigns also revealed negative freeboard comparable to those of IMBs in the seas around North Greenland and the Beaufort Sea. We further investigated the large-scale distribution of negative freeboard using NASA CryoSat-2 radar altimeter data, and the result indicates that except for the negative freeboard areas observed by IMBs and IceBridge, there are negative freeboards in other marginal seas of the Arctic Ocean. However, the comparison of the satellite data with the IMB data and IceBridge data shows that the Cryosat-2 data generally overestimate the extent and magnitude of the negative freeboard in the Arctic.展开更多
An imaginary plane method for calculation of radiative heat trensfer and its application in the freeboard of AFBC boiler is presented in this paper. The combustion reaction and particle concentration are taken into ac...An imaginary plane method for calculation of radiative heat trensfer and its application in the freeboard of AFBC boiler is presented in this paper. The combustion reaction and particle concentration are taken into account in this method. With is method, one-dimensional freeboard model for radiative heat transfer has been made. Results from this model have been compared with the experimental results of a 130 t/h AFBC boiler. The distribution of flue gas temperature and heat flux at the waterwell are obtained. It is shown that this model has the advantage of good accuracy and requiring less computation time. The applicability of the predicted results in the AFBC boiler design and operation was also discussed.展开更多
北极海冰变化受全球气候变化影响明显,海冰的变化不仅体现在面积上,而且也体现在厚度上。利用海冰干舷高度可以反演海冰厚度,冰、云和陆地高程卫星/地球科学激光测高系统（ice,cloud and land elevation satellite/geoscience laser alt...北极海冰变化受全球气候变化影响明显,海冰的变化不仅体现在面积上,而且也体现在厚度上。利用海冰干舷高度可以反演海冰厚度,冰、云和陆地高程卫星/地球科学激光测高系统（ice,cloud and land elevation satellite/geoscience laser altimeter system,ICESat/GLAS）提供了高精度的海冰高程信息。利用ICESat/GLAS测高数据,提取了2003～2008年部分时间段北极区域海冰的干舷高度,分析了2003～2008年间北极海冰季节性以及年际变化特征。结果表明,北极海冰干舷高度呈下降趋势,并且在2007年夏季减少趋势最为明显。对北极海冰在2007年迅速减少的原因进行了探讨,并利用仰视声呐实测数据对干舷高提取算法存在的系统性偏差进行了讨论与分析。展开更多
基金The National Natural Science Foundation of China under contract No.42076235.
文摘Antarctic sea ice is an important part of the Earth’s atmospheric system,and satellite remote sensing is an important technology for observing Antarctic sea ice.Whether Chinese Haiyang-2B(HY-2B)satellite altimeter data could be used to estimate sea ice freeboard and provide alternative Antarctic sea ice thickness information with a high precision and long time series,as other radar altimetry satellites can,needs further investigation.This paper proposed an algorithm to discriminate leads and then retrieve sea ice freeboard and thickness from HY-2B radar altimeter data.We first collected the Moderate-resolution Imaging Spectroradiometer ice surface temperature(IST)product from the National Aeronautics and Space Administration to extract leads from the Antarctic waters and verified their accuracy through Sentinel-1 Synthetic Aperture Radar images.Second,a surface classification decision tree was generated for HY-2B satellite altimeter measurements of the Antarctic waters to extract leads and calculate local sea surface heights.We then estimated the Antarctic sea ice freeboard and thickness based on local sea surface heights and the static equilibrium equation.Finally,the retrieved HY-2B Antarctic sea ice thickness was compared with the CryoSat-2 sea ice thickness and the Antarctic Sea Ice Processes and Climate(ASPeCt)ship-based observed sea ice thickness.The results indicate that our classification decision tree constructed for HY-2B satellite altimeter measurements was reasonable,and the root mean square error of the obtained sea ice thickness compared to the ship measurements was 0.62 m.The proposed sea ice thickness algorithm for the HY-2B radar satellite fills a gap in this application domain for the HY-series satellites and can be a complement to existing Antarctic sea ice thickness products;this algorithm could provide long-time-series and large-scale sea ice thickness data that contribute to research on global climate change.
基金supported by National Key Research and Development Program of China[Grant number 2021YFC2803301]China Europe Dragon 5 Cooperation Program[Grant number 59310]National Natural Science Foundation of China[Grant number 42071387].
文摘Icebergs are big chunks of ice floating on the ocean surface,and melting of icebergs contributes for the major part of freshwater flux into ocean.Dynamic monitoring of the icebergs in Antarctica and accurate estimation of their volume are important for predicting the trend of freshwater budget of the Southern Ocean.The iceberg freeboard is a key parameter for measuring the thickness and volume of an iceberg and is defined as the difference between the elevation of iceberg surface and sea level.So far,freeboards of icebergs have been successfully extracted using InSAR DEM,and the laser and radar altimeter.However,uncertainties exist in these results mainly caused by missed detection of small icebergs due to the spatially sparse and temporally incomplete data coverage.In addition to the above techniques,optical images can also be used to extract the iceberg freeboard based on its geometric relationship with shadow length,which can effectively compensate for the above shortcomings.Although the feasibility has been preliminarily presented,the precision and extensive application of shadow-height method deserves further research,such as estimating the basal melting of icebergs.In this work,we tested an optical image-based freeboard extraction method over icebergs in Prydz Bay,Antarctica.A normalized shadow pixel index(NSPI)is designed to identify iceberg shadows with different shapes in HY-1C/D CZI and Sentinel-2 MSI optical images.The iceberg freeboard can be determined with an acceptable precision(2 m)in optical images compared with laser altimeter(i.e.ICESat-2)measurements.Moreover,basal melting of icebergs has been assessed according to the variation of freeboard using repeated optical observations.The results indicate that icebergs in the study area were with a mean freeboard of about 56 m in early December 2022,and experienced a decrease in freeboard of 1.9 m within two months,in correspondence with the Antarctic seasonal trend.The methodological framework,therefore,turns out to be a reliable complementary approach to studying the iceberg freeboard in polar regions.
基金supported by the National Key Research and Development Program of China (No. 2018YFC1406104)the National Natural Science Foundation of China (Nos. 41425003 and 41971084)。
文摘The negative freeboard of sea ice(i.e., the height of ice surface below sea level) with subsequent flooding is widespread in the Southern Ocean, as opposed to the Arctic, due to the relatively thicker ice and thinner snow. In this study, we used the observations of snow and ice thickness from 103 ice mass balance buoys(IMBs) and NASA Operation IceBridge Aircraft Missions to investigate the spatial distribution of negative freeboard of Arctic sea ice. The Result showed that seven IMBs recorded negative freeboards, which were sporadically located in the seas around Northeast Greenland, the Central Arctic Ocean, and the marginal areas of the Chukchi–Beaufort Sea. The observed maximum values of negative freeboard could reach-0.12 m in the seas around Northeast Greenland. The observations from IceBridge campaigns also revealed negative freeboard comparable to those of IMBs in the seas around North Greenland and the Beaufort Sea. We further investigated the large-scale distribution of negative freeboard using NASA CryoSat-2 radar altimeter data, and the result indicates that except for the negative freeboard areas observed by IMBs and IceBridge, there are negative freeboards in other marginal seas of the Arctic Ocean. However, the comparison of the satellite data with the IMB data and IceBridge data shows that the Cryosat-2 data generally overestimate the extent and magnitude of the negative freeboard in the Arctic.
文摘An imaginary plane method for calculation of radiative heat trensfer and its application in the freeboard of AFBC boiler is presented in this paper. The combustion reaction and particle concentration are taken into account in this method. With is method, one-dimensional freeboard model for radiative heat transfer has been made. Results from this model have been compared with the experimental results of a 130 t/h AFBC boiler. The distribution of flue gas temperature and heat flux at the waterwell are obtained. It is shown that this model has the advantage of good accuracy and requiring less computation time. The applicability of the predicted results in the AFBC boiler design and operation was also discussed.
文摘北极海冰变化受全球气候变化影响明显,海冰的变化不仅体现在面积上,而且也体现在厚度上。利用海冰干舷高度可以反演海冰厚度,冰、云和陆地高程卫星/地球科学激光测高系统（ice,cloud and land elevation satellite/geoscience laser altimeter system,ICESat/GLAS）提供了高精度的海冰高程信息。利用ICESat/GLAS测高数据,提取了2003～2008年部分时间段北极区域海冰的干舷高度,分析了2003～2008年间北极海冰季节性以及年际变化特征。结果表明,北极海冰干舷高度呈下降趋势,并且在2007年夏季减少趋势最为明显。对北极海冰在2007年迅速减少的原因进行了探讨,并利用仰视声呐实测数据对干舷高提取算法存在的系统性偏差进行了讨论与分析。
