| Sea ice is an important part of the global climate system and plays an important role in regulating the balance of heat and radiation in the oceans and atmosphere.This is critical to understanding how the global climate system and how sea ice changes affect ecosystems for sea ice research.Operation IceBridge airborne data has high-resolution and high-precision characteristics,It's important and valuable for the research of Arctic sea ice changes.Using ATM altimetry data to calculate the five-year sea ice freeboard of the Arctic 2014-2018,analyzing the interannual variation and spatial distribution characteristics of sea ice freeboard in the Arctic winter.The key to calculating the sea ice freeboard freeboard is to obtain accurate local sea surface height.We analyzed four local sea surface height calculation methods commonly used by IceBridge,namely threshold/lowest point of elevation method,ATM L1 B data and DMS L1 B image combination method,sea surface Reflectance cutoff method,waveform feature method.Threshold of elevation method was adopted in the Arctic Beaufort Sea,and the Antarctic Weddell Sea experiment was carried out by combining the surface reflectance cutoff value and the elevation minimum point method.Considering the characteristics of various methods and the programmatic and accuracy requirements of sea ice freeboard extraction,this paper proposes the combination of surface reflectance cutoff method and elevation minimum point method to extract ATM L1 B in lead by surface reflectance R<0.25,eliminate the influence of irregular changes in geoid,dynamic terrain,tides,etc.,obtain the remaining elevation of ATM L1 B in leads,remove the abnormal value in the remaining elevation,and take the lowest 10 ATM L1 B point every 20 km along the track,to calculate the local sea surface height,the means of the local sea surface high standard deviation mean values in 2014-2018 are: 0.017 m,0.023 m,0.012 m,0.010 m,0.009 m,which meets the sea level high accuracy in the sea ice freeboard calculation.According to the requirements of the reference,the ATM L2 elevation data can obtain the sea ice freeboard after eliminating the influence of irregular changes in the geoid height,dynamic terrain,and tides.In order to verify the accuracy of the parameter selection during the calculation of the sea surface height in the Arctic and the accuracy of the sea ice freeboard calculation,Firstly,the DMS L1 B image synchronized with ATM L1 B was used to verify the feasibility and accuracy of surface reflectivity R<0.25 to extract the ATM L1 B in lead.There is a good coherence between sea ice freeboard caculated from this method on the Arctic track on March 21,2013 and that from the IDCSI4 product of NSIDC.The calculated sea ice freeboard by the method in this paper is 3-6cm higher than that of the IDCSI4.In the winter of 2014-2018,the mean values of the sea ice freeboard on the Arctic are: 0.55 m,0.56 m,0.37 m,0.46 m,0.40 m,which showed a decreasing trend overall.Dividing the route into the central Arctic and Beaufort,In the winter of 2014-2018,the sea ice freeboard in the central Arctic has been reduced by 0.17 m,and the Beaufort Sea has been reduced by 0.03 m.Sea ice is significantly reduced,and similar results are obtained from repeated track.In the winter of 2014-2018,the sea ice in the centra Arctic is thicker,and the sea ice freeboard is concentrated between 0.3 and 0.8 m,and the Beaufort sea ice freeboard is relatively thin,which is mainly concentrated in 0.2~0.5 m.Under the influence of ocean currents,air pressure and coastal areas,the thicker sea ice freeboards in winter are mainly distributed in the central Arctic near the Greenland and the Queen Elizabeth Islands. |
PDF Full Text Request