Satellite detection of increases in global land surface evapotranspiration during 1984–2007

Abstract

As a key component of digital earth, remotely sensed data provides the compelling evidence that the amount of water vapour transferred from the entire global surface to the atmosphere increased from 1984 to 2007. The validation results from the earlier evapotranspiration (ET) estimation algorithm based on net radiation (R _n ), Normalised Difference Vegetation Index (NDVI), air temperature and diurnal air temperature range (DTaR) showed good agreement between estimated monthly ET and ground-measured ET from 20 flux towers. Our analysis indicates that the estimated actual ET has increased on average over the entire global land surface except for Antarctica during 1984–2007. However, this increasing trend disappears after 2000 and the reason may be that the decline in net radiation and NDVI during this period depleted surface soil moisture. Moreover, the good correspondence between the precipitation trend and the change in ET in arid and semi-arid regions indicated that surface moisture linked to precipitation affects ET. The input parameters R _n , T _air, NDVI and DTaR show substantial spatio-temporal variability that is almost consistent with that of actual ET from 1984 to 2007 and contribute most significantly to the variation in actual ET.     

SUB-SATELLITE COLLECTION OF SUPPLEMENTAL REMOTE SENSING INFORMATION

This paper, the third in a series on the design, payloads, and operation of Soviet earth resource observation satellites [see MSRS, 1984, No. 4 and 1985, No. 1], describes the collection of supplemental sub-satellite information. More specifically, it outlines how the Soviets use satellite-synchronized aerial, ground, and water-borne sensors to gather auxiliary information used in the improvement of space imagery (data verification and correction, instrument calibration, etc.). A later section demonstrates procedures for selection and preparation of field test sites (for ground truth), and design of sub-satellite information measurement complexes. Translated from: Priroda Zemli iz kosmosa, A. P. Tishchenko and S. V. Viktorov, eds. Leningrad: Gidrometeoizdat, 1984, pp. 35-38.     

RADIO-TELEVISION COMPLEXES OF THE METEOR-PRIRODA SATELLITES

A second installment in a series of papers describing the technical basis for Soviet remote sensing from space focuses on the multispectral scanners of the “Meteor-Priroda” series of earth observation satellites. Designs of the various models are provided, as well as explanations of how such tasks as band separation, signal formation, and telemetry are performed. Translated from: Priroda Zemli iz kosmosa, A. P. Tishchenko and S. V. Viktorov, eds. Leningrad: Gidrometeoizdat, 1984, pp. 25-25-34.     

CHECKING TRAVERSE COMPUTATIONS

Abstract

Traverse Computations must be Checked.—A traverse is a chain of points connected by angular and linear measurements. The check on observations is provided by the agreement, obtained in computations, between the terminals of the traverse (terminal bearings and terminal co-ordinates) taken as fixed. This check is not sufficient, however, to serve as a check on the computations. As a matter of principle, computations should be free of errors; there are no limits of tolerance in computational work except for discrepancies arising from inaccuracy of last figures. Secondly, errors in computation may occur that are not revealed by the traverse misclosures, not to speak of compensational errors, the field for which is very favourable in traverse work.     

ON SELF-CALIBRATION TO DETERMINE SYSTEMATIC PHOTO-DISTORTION

The author investigates the use of “added parameters” in the adjustment of analytical photo-triangulation to compensate for unknown systematic errors in the system. The model selected for investigation is one proposed by D. Brown which, in the opinion of the author, contains terms which are highly correlated and, as such, degrade the solution. The discussion goes on to propose a statistical method for selection of parameters and provides numerical results of applications of the method proposed. Investigations show an improvement in accuracy of typical analytical triangulation to be in the order of about 1.1 to 3.0 times when using the method. Translated from: Geodeziya i kartografiya, 1984, No. 1, pp. 34-38.     

THE LANGUAGE OF MAPS AND ITS PRINCIPAL FEATURES

The author, head of the Department of Cartography at the Institute of Geography, analyzes the language of maps in terms of general semiotic principles. Using the similarity of processes in other language systems, he constructs a model of the language of maps that distinguishes two sublanguages, one reflecting the locational aspects of maps (coordinate grids, etc.), the other reflecting the map content. The discussion touches on the system of map symbols as a linguistic feature, analyzes the system of map language in terms of such linguistic features as vocabulary, grammar and syntax, and draws other analogies between the language of maps and other language systems. Translated from: Voprosy Geografii, No. 122/123, 1984, pp. 40-56.     

HIGHWAY TRANSITION CURVE DESIGN

Abstract

Any paper on transition curves would certainly be incomplete without the inclusion of a, section on the lemniscate, and whilst the writer personally prefers the Euler spiral as being easier to apply—once tables have beenprepared—it cannot be denied that within the range of tangential angle Φ used in ordinary highway practice, the two curves are so nearly alike in alignment that they must be equally satisfactory from the driver-vehicle point of view. The writer considers, however, that whilst users of the spiral generally seem to adopt a sort of "live and let live “attitude to the use of the lemniscate, exponents of the latter seem to have little good to say about the spiral. The main differences between the two curves are as follows:—(a) For the Euler spiral the intrinsio equation may be written lr = constant, whilst for the lemniscate the corresponding relationship is pr = constant, where p is the chord or polar ray AB in the writer's notation (see Fig. 1, p. 211). It follows from these two relationships that when the curves are flat as in the case of high speed spirals, the chord and arc-length are almost equal and the two curves must be almost identical also. It also follows, although not quite so obviously, that whilst the rate of change of curvature is exactly constant along the length of any Euler spiral, it eases off somewhat as a lemniscate gets sharper. This property will be mentioned again later.     

AN ELECTRO-OPTICAL METHOD FOR MEASURING COLOR CHARACTERISTICS ON PHOTOGRAPHS

This study presents a model of a color photograph as a transparent medium with particles of colored pigment embedded in it, with the characteristics of the pigment determining the hue of the picture, and the pigment concentration determining the purity of the color. On the basis of this proposed model, the study undertakes a theoretical examination of an automated method for determining the parameters of a color photograph (the hue and purity) based on scanning the picture with white light and analyzing the output signals of two photodetectors placed behind the photograph in question. Analytical formulae are derived which can be used to measure the color characteristics of a color photograph using the output signals of the photodetectors which, in turn, allows these measurements to be made automatically with simple equipment. Translated from: Izvestiya vuzov, Geodeziya i aerofoto-s'yemka, 1984, No. 2, pp. 65-70.     

DECORATIVE-APPLIED ART AND CARTOGRAPHY

The need to accelerate the development of map reading and interpretation skills by increasing the exposure of school-age children to maps and other cartographic images is now widely recognized. Two Soviet authors advocate a broader approach; namely, the expansion of decorative-commercial applications of cartography. Maps, in aesthetic and simplified form, should be used more widely as motifs for toys and household goods, articles of clothing, and displays of events and places of popular interest. The most basic properties of the earth (shape, natural colors, etc.) should be retained whenever possible, even when the maps themselves are highly abstract. Translated from: Geodezlya i kartografiya, 1984, No. 12, pp. 26-27.     

CURRENT PROBLEMS IN OCEAN MAPPING

The author, in a review of papers presented at the First All-Union Conference on the Geography and Mapping of the Oceans, outlines the present status and current trends of marine cartography in the USSR. Issues warranting increased attention include development of a systems approach for the mapping of marine ecosystems; improvement of methods and principles for the mapping of coastal zones, bottom relief, and shelf topography; and accelerated production of economic/resource maps of the oceans. Work now underway on a comprehensive, multi-volume A tlas of the Oceans reflects a Soviet concern with these issues. Translated from: Geodeziya i kartografiya, 1984, No. 12, pp. 38-42.     

THE POTENTIAL FOR VISUAL AND AUTOMATED INTERPRETATION OF FOREST VEGETATION WITH SCANNER IMAGERY

Feature classification maps derived from visual and automated methods of interpreting band-specific and composite imagery from the “Fragment” multispectral scanning system are compared in the study of vegetation and related features along the Gulf of Riga. The automated method, featuring a two-stage unsupervised/supervised classification algorithm developed at Moscow University (see MSRS, 1984, No. 3, pp. 255-261) provided for enhanced discrimination of wetland areas, farm land, and settlements, as well as for the elimination of extraneous components (especially the above) visually classified as deciduous forest. Translated from: Vestnilk Moskovskogo Universiteta, geografiya, 1988, No. 3, pp. 49-57 by Jay K. Mitchell, PlanEcon, Inc., Washington, DC 20005.     

TOPOLOGY AND THE TRANSFORMATION OF CARTOGRAPHIC IMAGES

A survey of the use of topologic concepts of space in map transofrmation supports the author's contention that so-called “transformed images” represent for the most part rather arbitrary distortions of conventional maps constructed in Euclidean space. This paper demonstrates how truly topologic images can be created “from scratch,” i.e., without manipulation of either the sizes or shapes of areal units on preexisting maps. Images created by quantitatively defining “graphic ratios” of areal units can thus be replicated by other cartographers with a minimum of subjectivity. Translated from: Geodeziya i kartografiya, 1984, No. 12, pp. 28-31.     

THE STUDY AND MAPPING OF HUMAN IMPACTS ON NATURE IN DIFFERENT REGIONS OF THE USSR USING SPACE IMAGERY

The authors present the results of experiments in the use of remote sensing imagery for construction of maps depicting human modification of nature. Four diverse areas within the USSR were selected as mapping sites, providing a broad range of environmental and land-use characteristics for investigation. Human impacts were most effectively mapped for two desert sites. The authors recommend combining satellite imagery with terrestrial spectrometric observations or color-infrared photography in investigations of environmental change in steppeland and forested territory. Translated from: Vestnik Moskovskogo Universiteta, geografiya, 1984, No. 6, pp. 11-18.     

Improving Geocode Accuracy with Candidate Selection Criteria

Geocoding systems typically use more than one geographic reference dataset to improve match rates and spatial accuracy, resulting in multiple candidate geocodes from which the single “best” result must be selected. Little scientific evidence exists for formalizing this selection process or comparing one strategy to another, leading to the approach used in existing systems which we term the hierarchy‐based criterion: place the available reference data layers into qualitative, static, and in many cases, arbitrary hierarchies and attempt a match in each layer, in order. The first non‐ambiguous match with suitable confidence is selected and returned as output. This approach assumes global relationships of relative accuracy between reference data layers, ignoring local variations that could be exploited to return more precise geocodes. We propose a formalization of the selection criteria and present three alternative strategies which we term the uncertainty‐, gravitationally‐, and topologically‐based strategies. The performance of each method is evaluated against two ground truth datasets of nationwide GPS points to determine any resulting spatial improvements. We find that any of the three new methods improves on current practice in the majority of cases. The gravitationally‐ and topologically‐based approaches offer improvement over a simple uncertainty‐based approach in cases with specific characteristics.     

ON JOEL MORRISON'S COMMENTS ON “CARTOGRAPHY IN THE WEST”

The Chair of the Moscow University Department of Cartography responds to comments made by the Editor-in-Chief on “Cartography in the West: An Analysis of Theoretical Views in Recent Years,” translated in Mapping Sciences and Remote Sensing, 1984, No. 2, pp. 118-124. Translated from: Vestnik Moskovskogo Universiteta, geografiya, 1985, No. 6, pp. 55-58.     

THE METEOR AND METEOR-PRIRODA EARTH OBSERVATION SATELLITES

This first installment in a series of papers extracted from a Soviet “manual” of remote sensing describes the design, operation, and payloads of the “Meteor” and “Meteor-Priroda” earth observation satellites-the latter as name given to “Meteor” satellites used for economic land-use studies, instead of their original meteorological applications. Issues such as orbit parameters, spatial resolution, scan width, and telemetry are also addressed. Translated from: Priroda Zemli iz kosmosa, A.P. Tishchenko and S.V. Viktorov, eds. Leningrad: Gidrometeoizdat, 1984, pp. 16-24.     

THE TRAINING OF AFRICAN SURVEYORS IN NIGERIA

Abstract

Whenever the Government wants to receive new students to be trained as surveyors for the Government Service it is usual for the public to be informed by means of a Gazette Notice outlining the conditions of entry into the Survey School which is attached to the Land and Survey Department. Nowadays students are admitted through the Government Higher College at Yaba by means of the Entrance Examination of that college. It is one of the conditions that before a candidate applies to take this Entrance Examination he must have passed his Cambridge School Certificate Examination, the Matriculation Examination of any British University, or its local equivalent, and must possess also a certificate of character.     

Ocean tidal parameters from starlette data

Starlette was launched in 1975 in order to study temporal variations in the Earth’s gravity field; in particular, tidal and Earth rotation effects. For the period April 1983 to April 1984 over12,700 normal points of laser ranging data to Starlette have been sub-divided into49 near consecutive 5–6 day arcs. Normal equations for each arc as obtained from a least-squares data reduction procedure, were solved for ocean tidal parameters along with other geodetic and geodynamic parameters. The tidal parameters are defined relative to Wahr’s body tides and Wahr’s nutation model and show fair agreement with other satellite derived results and those obtained from spherical harmonic decomposition of global ocean tidal models.     

“Yu laid out the lands:” georeferencing the Chinese Yujitu [Map of the Tracks of Yu] of 1136

In an historically contextualized overview of the earliest extant version of the Yujitu, engraved on stone under the Liu Yu regime but believed to be a copy of a Northern Song map, the paper analyzes factors that complicate its georeferencing. The paper introduces a new algorithm for nonlinear georeferencing, applying it to 45 points and finding that the placement of sites on the north-south axis must have been based on latitudinal observation. Despite the Yujitu's startlingly modern appearance, the paper finds that there are areas in which it reflects a loyalty to classical texts.     

Laser station coordinates and baselines from long-ARC and short-ARC analyses of starlette

Laser ranging to Starlette from April 1983 to April 1984 has been used to determine a coordinate set, UASC.ST1, of laser reference points for 18 tracking stations. The coordinates were derived by application of the least-squares data reduction procedure in a simultaneous solution along with geodynamic parameters for 49 near consecutive 5–6 day arcs. Comparisons with the University of Texas station coordinates,LSC 8112 andLSC 8402, and theRGO, Herstmonceux, coordinates,RGOSC.LG2, reveal consistency to near 30 cm in each coordinate. Furthermore, the translation vectors of the comparisons are not significantly different from zero indicating consistency in the implied origins of the systems. The period of analysis included seven occasions in which STARLETTE was tracked near simultaneously by three or four laser stations in North America. Using the short arcs as reference frameworks, station coordinates were determined by application of two contrasting methods, namely, a multi-arc simultaneous analysis and a weighted mean of the individual pass solutions. The former compared more favourably with baselines from the long-arc solution with anRMS error of near 16 cm. Comparison against theLSC 8402 coordinates confirmed that baselines accurate to within 15 cm can be achieved by satellite laser ranging to Starlette.