Assessment of total suspended sediment concentrations in Poyang Lake using HJ-1A/1B CCD imagery

We explored the potential of the environment and disaster monitoring and forecasting small satellite constellations (HJ-1A/1B satellites) charge-coupled device (CCD) imagery (spatial resolution of 30 m, revisit time of 2 days) in the monitoring of total suspended sediment (TSS) concentrations in dynamic water bodies using Poyang Lake, the largest freshwater lake in China, as an example. Field surveys conducted during October 17-26, 2009 showed a wide range of TSS concentration (3-524 mg/L). Atmospheric correction was implemented using the Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes (FLAASH) module in ENVI with the aid of aerosol information retrieved from concurrent Terra/Moderate Resolution Imaging Spectroradiometer (MODIS) surveys, which worked well at the CCD bands with relatively high reflectance. A practical exponential retrieval algorithm was created between satellite remote sensing reflectance and in-situ measured TSS concentration. The retrieved results for the whole water area matched the in-situ data well at most stations. The retrieval errors may be related to the problem of scale matching and mixed pixel. In three selected subregions of Poyang Lake, the distribution trend of retrieved TSS was consistent with that of the field investigation. It was shown that HJ-1A/1B CCD imagery can be used to estimate TSS concentrations in Poyang Lake over synoptic scales after applying an appropriate atmospheric correction method and retrieval algorithm.

Cell Breathing Scheme for Mega-Constellation Satellite Networks

Low earth orbit(LEO)mega-constellations can provide global low-latency high bandwidth coverage compared to the terrestrial network.The time-varying topology of satellite networks and the uneven traffic distribution lead to the mismatch between satellites and users,resulting in the waste of satellite resources and the degradation of user performance.Through negotiation with neighbors,the traditional terrestrial cell breathing continuously converges to the optimal cell size in the face of user tides,but this method is difficult to converge timely when facing rapid and extreme flow changes caused by the rapid movement of satellites.This paper presents a fast adaptive cell breathing scheme(Fa B)through sub-block division and satellite cell initialization and adjustment.Fa B divides the ground into sub-blocks according to the user density.When the satellite moves in the same sub-block,the step size of breathing is adjusted according to the cell size difference between the previous satellite and the current satellite.When the satellite switches between different sub-blocks,the initial value of the cell is determined according to the density of the new sub-block.In addition to negotiating with neighboring satellites,this scheme also introduces location information to directly adjust the parameters of cell breathing and decrease the time of cell breathing convergence.From the real constellation data-driven simulation,we conclude that Fa B can quickly adjust the size of the cell with the location changing,and the utilization rate is increased by 2.66 times compared to the method with no cell breathing,and by2.37 times compared to the method with cell breathing without location information.

Photometric analysis of a blue straggler eclipsing binary in the old open cluster NGC 2141

To understand the formation mechanism of blue stragglers in open clusters, we conducted a photometric analysis for a blue straggler eclipsing binary in the old open cluster NGC 2141. By using the least square fitting of times of minima, we derived the ephemeris and redetermined the orbital period of this system to be 0.6227 d. We have also done a photometric analysis for light curve with the Wilson-Devinney Code （2003）. The photometric solutions reveal a semi-detached binary with the second- ary component filling its Roche lobe. The photometric mass ratio MJMI （secondary/primary） was determined to be 0.190_＋0.002 and the ratio of V-band luminosity L2/LI（V） is about 0.033_＋0.001, which indicates the secondary component is overluminous. Thus, this blue straggler likely results from a substantial mass exchange between these two components.