Simultaneous measurements of sea surface temperature by GMS-1 and GMS-2

For accurate measurements of sea surface temperature in the 11 μm window region, it is necessary to eliminate the effect of atmospheric absorption. A technique using observations from different angles is one of the methods of eliminating this atmospheric effect. This technique is not possible at present, using a single satellite; but using two geosynchronous satellites, it is possible to observe a common area from two different elevation angles. To correct for atmospheric effects, therefore, we compared the infrared data obtained from observations at about the same time (less than a minute apart) on the equator using the GMS-1 and GMS-2 satellites which had about 20° longitudinal separation. It was found that if the infrared spectral wavelength channel of one geosynchronous satellite is selected to be different from that of the other, it is possible to improve the two-satellite observation technique of estimating water vapor content in a tropical atmosphere. This technique corresponds to split window measurements by the AVHRR radiometer on board the NOAA-7 satellite.     

In-orbit assessment of laser retro-reflector efficiency onboard high orbiting satellites

The navigation and geodetic satellites that orbit the Earth at altitudes of approximately 20,000 km are tracked routinely by many of the Satellite Laser Ranging (SLR) stations of the International Laser Ranging Service (ILRS). In order to meet increasing demands on SLR stations for daytime and nighttime observations, any new mission needs to ensure a strong return signal so that the target is easily acquirable. The ILRS has therefore set a minimum effective cross-section of 100 million square metres for the on-board laser retro-reflector arrays (LRAs) and further recommends the use of ‘uncoated’ cubes in the arrays. Given the large number of GNSS satellites that are currently supported by SLR, it is informative to make an assessment of the relative efficiencies of the various LRAs employed. This paper uses the laser ranging observations themselves to deduce and then compare the efficiencies of the LRAs on the COMPASS-M1 navigation satellite, two satellites from the GPS and three from the GLONASS constellations, the two GIOVE test satellites from the upcoming Galileo constellation, the two Etalon geodetic spheres and the geosynchronous communications test satellite, ETS-8. All the LRAs on this set of satellites employ back-coated retro-reflector cubes, except those on the COMPASS-M1 and ETS-8 vehicles which are uncoated. A measure of return signal strength, and thus of LRA-efficiency, is calculated using the laser-range full-rate data archive from 2007 to 2010, scaled to remove the effects of variations in satellite range, atmospheric attenuation and retro-reflector target total surface area. Observations from five SLR stations are used in this study; they are Herstmonceux (UK), Yarragadee (Australia), Monument Peak and McDonald (USA) and Wettzell (Germany). Careful consideration is given to the treatment of the observations from each station in order to take account of local working practices and system upgrades. The results show that the uncoated retro-reflector cubes offer significant improvements in efficiency.     

Validation of 9.6 μm ozone transmittances by spectral radiance satellite measurements

The accuracy of atmospheric transmittances is important in remote sensing applications. In this paper the atmospheric ozone transmittances in the 1042 cm^?1 ozone band were calculated for different temperatures and ozone profiles using line-by-line integration method. The absorption line parameters were taken from McClatchey's line parameter compilation. The transmittances were used to derive the main characteristics of the atmospheric ozone profile and the total ozone amount from radiance measurements of Meteor satellites.     

Satellite remotely-sensed land surface parameters and their climatic effects for three metropolitan regions

By using both high-resolution orthoimagery and medium-resolution Landsat satellite imagery with other geospatial information, several land surface parameters including impervious surfaces and land surface temperatures for three geographically distinct urban areas in the United States – Seattle, Washington, Tampa Bay, Florida, and Las Vegas, Nevada, are obtained. Percent impervious surface is used to quantitatively define the spatial extent and development density of urban land use. Land surface temperatures were retrieved by using a single band algorithm that processes both thermal infrared satellite data and total atmospheric water vapor content. Land surface temperatures were analyzed for different land use and land cover categories in the three regions. The heterogeneity of urban land surface and associated spatial extents were shown to influence surface thermal conditions because of the removal of vegetative cover, the introduction of non-transpiring surfaces, and the reduction in evaporation over urban impervious surfaces. Fifty years of in situ climate data were integrated to assess regional climatic conditions. The spatial structure of surface heating influenced by landscape characteristics has a profound influence on regional climate conditions, especially through urban heat island effects.     

The United States operational polar-orbiting satellite series,TIROS-N

The U.S. launched the first of its new series of polar-orbiting, operational satellites, named TIROS-N, on 13 October 1978. The second, named NOAA-A, was launched on 27 June 1979. Together they comprise the operational system since from an average altitude of 840 km two satellites are required to provide global coverage in the equatorial zone. Operational products for FGGE (atmospheric temperature profiles, sea surface temperature analysis, and other data) are discussed and compared with prior performance. New uses in support of oceanology (Service ARGOS) are described.     

Surface temperature estimation in Singhbhum Shear Zone of India using Landsat-7 ETM+ thermal infrared data

Land surface temperature (LST) is an important factor in global change studies, heat balance and as control for climate change. A comparative study of LST over parts of the Singhbhum Shear Zone in India was undertaken using various emissivity and temperature retrieval algorithms applied on visible and near infrared (VNIR), and thermal infrared (TIR) bands of high resolution Landsat-7 ETM+ imagery. LST results obtained from satellite data of October 26, 2001 and November 2, 2001 through various algorithms were validated with ground measurements collected during satellite overpass. In addition, LST products of MODIS and ASTER were compared with Landsat-7 ETM+ and ground truth data to explore the possibility of using multi-sensor approach in LST monitoring. An image-based dark object subtraction (DOS3) algorithm, which is yet to be tested for LST retrieval, was applied on VNIR bands to obtain atmospheric corrected surface reflectance images. Normalized difference vegetation index (NDVI) was estimated from VNIR reflectance image. Various surface emissivity retrieval algorithms based on NDVI and vegetation proportion were applied to ascertain emissivities of the various land cover categories in the study area in the spectral range of 10.4–12.5 μm. A minimum emissivity value of about 0.95 was observed over the reflective rock body with a maximum of about 0.99 over dense forest. A strong correlation was established between Landsat ETM+ reflectance band 3 and emissivity. Single channel based algorithms were adopted for surface radiance and brightness temperature. Finally, emissivity correction was applied on ‘brightness temperature’ to obtain LST. Estimated LST values obtained from various algorithms were compared with field ground measurements for different land cover categories. LST values obtained after using Valor’s emissivity and single channel equations were best correlated with ground truth temperature. Minimum LST is observed over dense forest as about 26 °C and maximum LST is observed over rock body of about 38 °C. The estimated LST showed that rock bodies, bare soils and built-up areas exhibit higher surface temperatures, while water bodies, agricultural croplands and dense vegetations have lower surface temperatures during the daytime. The accuracy of the estimated LST was within ±2 °C. LST comparison of ASTER and MODIS with Landsat has a maximum difference of 2 °C. Strong correlation was found between LST and spectral radiance of band 6 of Landsat-7 ETM+. Result corroborates the fact that surface temperatures over land use/land cover types are greatly influenced by the amount of vegetation present.     

The NOAA satellites: A largely neglected tool in the land sciences

The NOAA satellite system comprises the polar-orbiting satellites which provide image data twice a day, and the geostationary satellites, which provide image data every 30 minutes. Data is provided in the visible, near infrared, and middle and far thermal infrared at 1 km resolution from the polar-orbiting satellites and in the visible at 1-km resolution and in the far thermal infrared at 8 km resolution from the geostationary satellites. Applications described include monitoring tectonic lineaments in Alaska, monitoring the Greenland Ice Sheet, mapping geomorphology in the Dakotas and monitoring volcano eruptions. Applications of the Heat Capacity Mapping Mission described include discriminating rock types and indications of mineral deposits. Current research into Land Sciences Applications are discussed and recommendations made for further areas of research.     

Estimating low resolution gravity fields at short time intervals to reduce temporal aliasing errors

The Gravity Recovery and Climate Experiment (GRACE) satellite mission has been estimating temporal changes in the Earth’s gravitational field since its launch in 2002. While it is not yet fully resolved what the limiting source of error is for GRACE, studies on future missions have shown that temporal aliasing errors due to undersampling signals of interest (such as hydrological variations) and errors in atmospheric, ocean, and tide models will be a limiting source of error for missions taking advantage of improved technologies (flying drag-free with a laser interferometer). This paper explores the option of reducing the effects of temporal aliasing errors by directly estimating low degree and order gravity fields at short time intervals, ultimately resulting in data products with improved spatial resolution. Three potential architectures are considered: a single pair of polar orbiting satellites, two pairs of polar orbiting satellites, and a polar orbiting pair of satellites coupled with a lower inclined pair of satellites. Results show that improvements in spatial resolution are obtained when one estimates a low resolution gravity field every two days for the case of a single pair of satellites, and every day for the case of two polar pairs of satellites. However, the spatial resolution for these cases is still lower than that provided by simply destriping and smoothing the solutions via standard GRACE post-processing techniques. Alternately, estimating daily gravity fields for the case of a polar pair of satellites coupled with a lower inclined pair results in solutions with superior spatial resolution than that offered by simply destriping and smoothing the solutions.     

小行星表面有机物的红外光谱探测方法

小行星的有机物记录了太阳系早期有机物的形成发展历史,为地球早期生命前体出现的研究提供了重要依据,对于研究生命起源和演化具有重要意义.本文综合分析了小行星表面可能存在的有机物成分、种类及其赋存状态,利用红外光谱开展地面模拟实验,探讨有机物的红外光谱特征及其影响因素.结果表明,不同类型有机物的红外光谱特征与其类型、结构、温...     

Remote sensing applications in the meteorology and operational hydrology programmes of WMO

Remote sensing from satellites continues to have a very large impact on the activities of the World Meteorological Organization (WMO) and continues to provide very great benefits to meteorological services throughout the world. Meteorological satellites provide remotely sensed data which can be converted into meteorological measurements such as cloud cover, cloud motion vectors, surface temperature, vertical profiles of atmospheric temperature and humidity, snow and ice cover, ozone and various radiation measurements. The meteorological satellites are part of the global operations of the World Weather Watch Programme which serves as the basic programme of the WMO by supporting other programmes and activities. Satellite measurements are critical to the success of many different components in the World Climate Programme. Special projects are being designed for the 1990s to take advantage of the data from satellite systems designed primarily to provide land or ocean observations. The Applications of Meteorology Programme makes use of remotely sensed data to provide products and services to agricultural, aeronautical and marine activities. The transfer of knowledge and technology in satellite remote sensing applications are important elements of the Technical Co-operation and the Education and Training Programmes.     

Verification of satellite observations of stratospheric minor constituents

The TIROS-N operational meteorological satellite observing system will have the capability of determining global ozone amounts from two instruments by 1985. The TIROS Operational Vertical Sounder (TOVS) yields total ozone amounts through measurements of atmospheric infrared radiances. The Solar Backscatter Ultraviolet (SBUV/2) spectrometer yields total ozone amounts and vertical ozone profiles through measurements of the solar ultraviolet radiation backscattered by the atmosphere. The current operations plan calls for single satellites containing both instruments system with local afternoon equator crossing times. They will be launched at approximately 18 month intervals.The satellite ozone products will require verification using commonly accepted references. For total ozone, Dobson spectrophotometer determinations are to be used. For vertical profiles, no clear choice now exists among balloon-launched chemical sondes, rocket-launched optical sondes or Dobson Umkehr measurements. The applicability and use of these measurement systems are discussed with emphasis on the need for the verification data consistent with the operational satellite lifetimes.Another major source of data for verification is other satellite systems. Comparisons of vertical ozone profiles from several concurrent satellites is discussed. This includes results from SAGE, LIMS and SBUV.     

Strategy for early detection of climatic change

A general strategy for detection of climatic changes of stratospheric temperatures is discussed in the light of expected short-term and long-term natural and spurious (instrumentally-induced) variability. The effects of the brevity of both the radiosonde record and the satellite sounding record are stressed, and the need is emphasised for homogeneous time-series from satellites as well as from sondes.The general principles are illustrated by means of an attempt to detect climatic changes in the extratropical upper troposphere and lower stratosphere using radiosonde data for approximately the past 25 years. It is shown that, even in the absence of instrumental shortcomings, a further 35 years of radiosonde data, or 20–25 years of satellite sounding data, are needed for detection of temperature trends of the size indicated by global circulation models for the present rate of increase of concentration of atmospheric carbon dioxide.     

Monitoring global surface temperature variations using cloud data sets

One of the by-products of cloud data sets such as that of the International Satellite Cloud Climatology Project (ISCCP) is global information on longwave window brightness temperatures for clear skies. These brightness temperatures depend mainly on the actual surface temperature with only a slight dependence on atmospheric water vapor. Thus, it may be possible to monitor long-term temperature variations using such data. The current methods for such monitoring depend on conventional surface observations and are subject to uncertainties due to inadequate spatial sampling. To test this idea monthly clear sky brightness temperatures from the six-year Nimbus-7 cloud data set are analyzed and compared to conventional estimates of surface temperature fluctuations.     

Measuring atmospheric density using GPS–LEO tracking data

We present a method to estimate the total neutral atmospheric density from precise orbit determination of Low Earth Orbit (LEO) satellites. We derive the total atmospheric density by determining the drag force acting on the LEOs through centimeter-level reduced-dynamic precise orbit determination (POD) using onboard Global Positioning System (GPS) tracking data. The precision of the estimated drag accelerations is assessed using various metrics, including differences between estimated along-track accelerations from consecutive 30-h POD solutions which overlap by 6 h, comparison of the resulting accelerations with accelerometer measurements, and comparison against an existing atmospheric density model, DTM-2000. We apply the method to GPS tracking data from CHAMP, GRACE, SAC-C, Jason-2, TerraSAR-X and COSMIC satellites, spanning 12 years (2001–2012) and covering orbital heights from 400 km to 1300 km. Errors in the estimates, including those introduced by deficiencies in other modeled forces (such as solar radiation pressure and Earth radiation pressure), are evaluated and the signal and noise levels for each satellite are analyzed. The estimated density data from CHAMP, GRACE, SAC-C and TerraSAR-X are identified as having high signal and low noise levels. These data all have high correlations with anominal atmospheric density model and show common features in relative residuals with respect to the nominal model in related parameter space. On the contrary, the estimated density data from COSMIC and Jason-2 show errors larger than the actual signal at corresponding altitudes thus having little practical value for this study. The results demonstrate that this method is applicable to data from a variety of missions and can provide useful total neutral density measurements for atmospheric study up to altitude as high as 715 km, with precision and resolution between those derived from traditional special orbital perturbation analysis and those obtained from onboard accelerometers.     

Stereoscopic imaging from polar orbit and synthetic stereo imaging

The photogrammetric determination of cloud top heights from stereoscopic satellite images seems to be a very good solution to this hitherto unresolved problem. Whereas in the U.S.A., stereoscopic imaging is done by use of geosynchronous weather satellites, in Europe such a system cannot be used because there is only one geosynchronous satellite (METEOSAT). An alternative could be a Stero Line Scanner (SLS) operating on a polar orbiter.SLS would scan twice, forward and backward, producing in this way two image strips for steroscopic viewing and photogrammetric measurements from pole to pole. Because of the cloud motion between the two scans, a SLS needs additional independent height information for reference points, e.g. from a Laser Ranger (LAR). The advantage of this method is that cloud motion, and therefore wind, can also be determined for these reference points. Another solution is a system of two SLS satellites flying one after the other and scanning the same area simultaneously. This allows cloud motion determination across the whole image. The use of infrared channels also allows night operation and provides additional data such as improved seas surface temperatures.The DFVLR is currently studying these problems. Synthetic stereoscopic imaging is being used in a forerunner programm to the SLS project and also for simulation in SLS studies.     

Sea surface temperature measurement from satellites: Validation and accuracy

A review of the latest published results concerning the accuracy of satellite derived sea surface temperature (SST) estimation is presented. Two types of platforms are considered : orbiting satellites and geosynchronous satellites and the accuracies that may now be expected from such systems are reported. This review emphasizes the impressive improvement in global mapping of SST obtained from the Advanced Very High Resolution Radiometer (AVHRR) on NOAA's operational polar satellites. Tests of the AVHRR SST's against a high reliability data set consisting of buoys, bathythermographs and research ship reports indicate biases of < 0.1°C and RMS differences of < 0.75°C (McClain [1]). Particular attention is also paid to a method adding along track scanning capability to the present multichannel AVHRR technique. This method is demonstrated owing to the coupling of an orbiting satellite (TIROS-N) and a geosynchronous satellite (METEOSAT). Another type of coupling of two such platforms is also presented in connection with the advent of geostationary satellites equipped with a vertical sounding capability, such as GOES-4.     

Simulation of the land surface temperature from moon-based Earth observations

The land surface temperature (LST) is a key parameter for the Earth’s energy balance. As a natural satellite of the Earth, the orbital of the moon differs from that of current Earth observation satellites. It is a new way to measure the land surface temperature from the moon and has many advantages compared with artificial satellites. In this paper, we present a new method for simulating the LST measured by moon-based Earth observations. Firstly, a modified land-surface diurnal temperature cycle (DTC) method is applied to obtain the global LST at the same coordinated universal time (UTC) using the Moderate Resolution Imaging Spectroradiometer (MODIS) LST products. The lunar elevation angles calculated using the ephemeris data (DE405) from the Jet Propulsion Laboratory (JPL) were then applied to simulate the Earth coverage observed from the moon. At the same time, the modified DTC model was validated using in situ data, MODIS LST products, and the FengYun-2F (FY-2F) LST, respectively. The results show that the fitting accuracy (root-mean-square error, RMSE) of the modified DTC model is not greater than 0.72?°C for eight in situ stations with different land cover types, and the maximum fitting RMSE of the modified model is smaller than that of current DTC models. By the comparison of the simulated LST with MODIS and FY-2F LST products, the errors of the results were feasible and accredited, and the simulated global LST has a reasonable spatiotemporal distribution and change trend. The simulated LST data can therefore be used as base datasets to simulate the thermal infrared imagery from moon-based Earth observations in future research.     

气球卫星1990—81B和1990－81C的轨道变化和高层大气密度的测定

本文测定给出我国首次发射的专用于高层大气探测的两颗气球卫星DQ-1A(1990-81B)和DQ-1B(1990-81C)整个寿命期间的轨道变化,以及利用轨道衰变率,采用适合气球卫星近国轨道反测密度的一种方法,获得500-900km高度范围内太阳峰年期间的高层大气密度及其变化。结果表明,同时发射的两颗面积质量比不同的气球卫星所测定的高层大气密度及其变化非常一致,且明显地显示密度随太阳活动逐日的和27天周期性的变化。本文将密度测定结果与高层大气模型进行了比较和分析。      

Synergetic retrieval of terrestrial AOD from MODIS images of twin satellites Terra and Aqua

Aerosol optical depth (AOD) is one of the most important indicators of atmospheric pollution. It can be retrieved from satellite imagery using several established methods, such as the dark dense vegetation method and the deep blue algorithm. All of these methods require estimation of surface reflectance prior to retrieval, and are applicable to a certain pre-designated type of surface cover. Such limitations can be overcome by using a synergetic method of retrieval proposed in this study. This innovative method is based on the fact that the ratio K of surface reflectance at different angles/geometries is independent of wavelength as reported by Flowerdew and Haigh (1995). An atmospheric radiative transfer model was then established and resolved with the assistance of the ratio K obtained from two Moderate Resolution Imaging Spectroradiometer (MODIS) spectral bands acquired from the twin satellites of Terra and Aqua whose overpass is separated by three hours. This synergetic method of retrieval was tested with 20 pairs of MODIS images. The retrieved AOD was validated against the ground observed AOD at the Taihu station of the AErosol RObotic NETwork (AERONET). It is found that they are correlated with the observations at a coefficient of 0.828 at 0.47 μm and 0.921 at 0.66 μm wavelengths. The retrieved AOD has a mean relative error of 25.47% at 0.47 μm and 24.3% at 0.66 μm. Of the 20 samples, 15 and 17 fall within two standard error of the line based observed AOD data on the ground at the 0.47 μm and 0.66 μm, respectively. These results indicate that this synergetic method can be used to reliably retrieve AOD from the twin satellites MODIS images, namely Terra and Aqua. It is not necessary to determine surface reflectance first.     

Estimation of vertically integrated water vapor in Hungary using MODIS imagery

Information about the amount and spatial structure of atmospheric water vapor is essential in understanding meteorology and the Earth environment. Space-borne remote sensing offers a relatively inexpensive method to estimate atmospheric water vapor in the form of integrated water vapor (IWV). The research activity reported in the present paper is based on the data acquired by the HRPT/MODIS (High Resolution Picture Transmission, MODerate resolution Imaging Spectroradiometer) receiving station established in Budapest (Hungary) by the Space Research Group of the Eötvös Loránd University. Integrated water vapor is estimated by the remotely sensed data of the MODIS instrument with different methods and also by the operational numerical weather prediction model of the European Centre for Medium-Range Weather Forecasts (ECMWF). Radiosonde data are used to evaluate the accuracy of the different IWV fields though it has been pointed out that the in situ data also suffers from uncertainties. It was found that both the MODIS and the ECMWF based fields are of good accuracy. The satellite data represent finer scale spatial structures while the ECMWF data have a relatively poor spatial resolution. The high quality IWV fields have proved to be useful for radiative transfer studies such as the atmospheric correction of other satellite data from times different than the overpass times of satellites Terra/Aqua and the forecast times of the model data. For this purpose the temporal variability of IWV is scrutinized both using ECMWF and MODIS data. Taking advantage of Terra and Aqua overpasses, the mean rate of change of IWV estimated by the near infrared method was found to be 0.47 ± 0.45 kg m⁻² h⁻¹, while it was 0.13 ± 0.65 kg m⁻² h⁻¹ based on the infrared method. The numerical weather prediction model’s analysis data estimated −0.01 ± 0.13 kg m⁻² h⁻¹ for the mean growth rate, while using forecast data it was 0.24 ± 0.18 kg m⁻² h⁻¹. MODIS data should be used when available for the estimation of the IWV in other studies. If no satellite data are available, or available data are only from one overpass, ECMWF based IWV can be used. In this case the analysis fields (or the satellite field) should be used for temporal extrapolation but the rate of change should be calculated from the forecast data due to its higher temporal resolution.