Combining Lidar Elevation Data and IKONOS Multispectral Imagery for Coastal Classification Mapping

This article studies the effect of airborne lidar (surface) elevation data on the classification of multispectral IKONOS images over a coastal area. The lidar data and IKONOS images are treated as independent multiple bands to conduct the classification. To do so, the lidar elevation data is first resampled to the same ground spacing interval and stretched to the same radiometric range as the IKONOS images. An unsupervised classification based on the ISODATA algorithm is then used to determine a class schema of six classes: road, water, marsh, roof, tree, and sand. Training sites and checking sites are selected over the lidar-IKONOS merged data set for the subsequent supervised classification and quality evaluation. The complete confusion matrices and average quality indices are presented to assess and compare the classification results. It is shown that the inclusion of the lidar elevation data benefits the separation of classes that have similar spectral characteristics, such as roof and road, water and marsh. The overall classification errors, especially the false positive errors, are reduced by up to 50%. Moreover, by using the lidar elevation data, the classification results show more realistic and homogeneous distribution of geographic features. This property will benefit the subsequent vectorization of the classification maps and the integration of the vector data into a geographical information system.     

SPOT 5卫星遥感影像在土地利用数据库系统更新中的应用

随着国民经济的快速发展,土地现状变更十分频繁,如何保持数据库系统的现势性成为国土资源管理部门的一项重要工作。该文介绍了利用卫星遥感数据对土地利用数据库变更的系统设计、实现方法及结果,说明了利用遥感卫星数据对数据库进行更新的优势。     

2008年以来青藏高原春季大气温度逆转趋势及其与臭氧总量变化之间的可能联系

利用ERA-Interim和MERRA-2再分析资料,考察1980—2017年青藏高原大气温度变化趋势和规律,年、季、月不同时间尺度分析结果均揭示2008年以来青藏高原春季大气温度变化呈现逆转趋势：高原上空平流层下部150~50 hPa呈现明显的增温趋势（1.0~2.7℃/10a),对流层上部300~175 hPa呈现明显的降温趋势（-3.1~-1.0℃/10a),这与此前的大气温度变化趋势完全相反。利用TOMS和OMI卫星臭氧遥感资料,考察同期青藏高原臭氧总量变化特征,表明2008年以来青藏高原臭氧总量也表现出逆转的增加趋势,与大气温度逆转趋势吻合,从冬末至春季各月均有显著增加趋势,尤以5月臭氧总量增加速率最大,达13.7 DU/10a。青藏高原春季大气温度变化趋势与同期臭氧总量变化特征紧密相关,2008年后臭氧总量的快速恢复可能是引起大气温度逆转趋势的一个重要影响因素。     

Remote sensing for mapping natural habitats and their conservation status – New opportunities and challenges

Safeguarding the diversity of natural and semi-natural habitats in Europe is one of the aims set out by the Habitats Directive (Council Directive 92/43/EEC on the conservation of natural habitats and of wild fauna and flora) and one of the targets of the European 2020 Biodiversity Strategy, and is to be accomplished by maintaining a favourable conservation status. To reach this aim a high-level understanding of the distribution and conditions of these habitats is needed. Remote sensing can considerably contribute to habitat mapping and their observation over time. Several European projects and a large number of scientific studies have addressed the issue of mapping and monitoring natural habitats via remote sensing and the deriving of indicators on their conservation status. The multitude of utilized remote sensing sensors and applied methods used in these studies, however, impede a common understanding of what is achievable with current state-of-the-art technologies. The aim of this paper is to provide a synthesis on what is currently feasible in terms of detection and monitoring of natural and semi-natural habitats with remote sensing. To focus this endeavour, we concentrate on those studies aimed at direct mapping of individual habitat types or discriminating between different types of habitats occurring in relatively large, spatially contiguous units. By this we uncover the potential of remote sensing to better understand the distribution of habitats and the assessment of their conservation status in Europe.     

Evaluation of SPOT imagery for the estimation of grassland biomass

In many regions, a decrease in grasslands and change in their management, which are associated with agricultural intensification, have been observed in the last half-century. Such changes in agricultural practices have caused negative environmental effects that include water pollution, soil degradation and biodiversity loss. Moreover, climate-driven changes in grassland productivity could have serious consequences for the profitability of agriculture. The aim of this study was to assess the ability of remotely sensed data with high spatial resolution to estimate grassland biomass in agricultural areas. A vegetation index, namely the Normalized Difference Vegetation Index (NDVI), and two biophysical variables, the Leaf Area Index (LAI) and the fraction of Vegetation Cover (fCOVER) were computed using five SPOT images acquired during the growing season. In parallel, ground-based information on grassland growth was collected to calculate biomass values. The analysis of the relationship between the variables derived from the remotely sensed data and the biomass observed in the field shows that LAI outperforms NDVI and fCOVER to estimate biomass (R² values of 0.68 against 0.30 and 0.50, respectively). The squared Pearson correlation coefficient between observed and estimated biomass using LAI derived from SPOT images reached 0.73. Biomass maps generated from remotely sensed data were then used to estimate grass reserves at the farm scale in the perspective of operational monitoring and forecasting.     

A combined deficit index for regional agricultural drought assessment over semi-arid tract of India using geostationary meteorological satellite data

The untimely onset and uneven distribution of south-west monsoon rainfall lead to agricultural drought causing reduction in food-grain production with high vulnerability over semi-arid tract (SAT) of India. A combined deficit index (CDI) has been developed from tri-monthly sum of deficit in antecedent rainfall and deficit in monthly vegetation vigor with a lag period of one month between the two. The formulation of CDI used a core biophysical (e.g., NDVI) and a hydro-meteorological (e.g., rainfall) variables derived using observation from Indian geostationary satellites. The CDI was tested and evaluated in two drought years (2009 and 2012) within a span of five years (2009–2013) over SAT. The index was found to have good correlation (0.49–0.68) with standardized precipitation index (SPI) computed from rain-gauge measurements but showed lower correlation with anomaly in monthly land surface temperature (LST). Significant correlations were found between CDI and reduction in agricultural carbon productivity (0.67–0.83), evapotranspiration (0.64–0.73), agricultural grain yield (0.70–0.85). Inconsistent correlation between CDI and ET reduction was noticed in 2012 in contrast to consistent correlation between CDI and reduction in carbon productivity both in 2009 and 2012. The comparison of CDI-based drought-affected area with those from existing operational approach showed 75% overlapping regions though class-to-class matching was only 40–45%. The results demonstrated that CDI is a potential indicator for assessment of late-season regional agricultural drought based on lag-response between water supply and crop vigor.     

资源三号卫星影像融合算法对比分析

我国第一颗高精度民用立体测绘卫星——资源三号卫星搭载了2.1m分辨率的全色相机和5.8m分辨率的多光谱相机,针对资源三号影像研究有效的影像融合算法对于提高资源三号的影像质量和应用范围具有很大意义。文章分析了Pansharp、Gram-Schmidt、Modified IHS、改进的SFIM和Brovey 5种融合算法,梳理了影像融合的质量评价指标体系,采用资源三号卫星影像覆盖的农田、城区、林地、裸地等不同类型的区域开展几种融合算法试验,并对试验结果进行了分析评价。实验结果表明,5种融合算法中,Pansharp融合算法对资源三号影像数据融合效果最优,Gram-Schmidt融合算法次之,其次为Modified IHS影像融合算法,改进的SFIM融合算法和Brovey融合算法融合效果较差。     

卫星导航接收机中多波束抗干扰技术

抗干扰是卫星导航接收机中一项重要的技术。提出了一种卫星导航接收机中的新型多波束抗干扰方法,该方法能够较好地兼顾零陷深度与卫星信号增益的矛盾,达到抑制干扰的同时增强卫星信号强度的目的。通过大量仿真实验分析了波束数目、波束分配方式以及波束指向偏差对抗干扰性能的影响。仿真结果和性能分析验证了该方法的有效性和可行性。     

Altimetry and transponder ground simulation experiment

We have designed and built a compact demonstrator unit for the investigation of altimetry and transponder applications. A small light-weight breadboard carries a compact frequency doubled Nd:YAG pulse laser, an afocal beam expansion optics, a small receiver telescope with spectral and spatial filter arrangements and a sensitive photo-detector. The output laser energy can be as high as 45 mJ with a pulse-width of 3 ns and the telescope aperture is 10 cm. Simulations [Degnan, J.J., 2006. Simulating interplanetary transponder and laser communications experiments via dual station ranging to SLR satellites. In: Proceedings of the 15th International Workshop on Laser Ranging, Canberra, Australia, pp. 457-462] suggested that the link margin for low Earth orbiting satellites (LEO) is comfortable. Successful satellite laser ranging from this dual-station experiment in several different configurations was achieved up to the MEO orbit in a 10 day provisional installation.     

B-Pol: detecting primordial gravitational waves generated during inflation

B-Pol is a medium-class space mission aimed at detecting the primordial gravitational waves generated during inflation through high accuracy measurements of the Cosmic Microwave Background polarization. We discuss the scientific background, feasibility of the experiment, and implementation developed in response to the ESA Cosmic Vision 2015-2025 Call for Proposals. See for the full list of collaboration members and a full copy of the B-Pol proposal.