Geography

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An Evolution of Land Use in Kent County, Maryland
(1953) Singleton, Carey B. Jr; Van Royen, William; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
The object of this study is to determine the land use changes that have taken place in Kent County, located on the Eastern Shore of Maryland (See Fig. 1) with emphasis on recent land use changes. The principal objectives of this study will be to ascertain, analyze, and review the evolution of land utilization in Kent County. A major trend within the past ten years has been toward a decreasing number of farms and, at the same time, a decreasing number of people gainfully employed in agriculture. This trend has resulted in the displacement of agricultural earners by fa.rm machinery and farm consolidations. An increase in the average size of farms is due to "outsiders" - business men from out-of-state -- who have established themselves in the county by buying and combining principally waterfront property. Thus large estates are formed along with the restoration of Colonial homes. This type of land tenure has been bringing about utilization of the land in the form of large dairy and beef herds. Kent County has the smallest number of farms of all the counties in Maryland but it has the largest average farm size in the state. This is an area of predominantly large dairy farms with highly mechanized machinery and equipment. The major trend in the last 25 years has been from cash grain to livestock raising which has resulted from the growth of dairying. The pattern of field crops has also changed from cash grains to feed grains for the large dairy herds. This study has been accomplished through the use of field work historical data, tables, maps, and photographs. The assumption can be made that greater permanency and stability in land use may be assured by utilizing the land for what it is best suited to produce. In an agricultural county, such as Kent, the retention of the soil, maintenance of its fertility, and the productivity are fundamental and therefore, the outstanding problems of optimum land utilization in the county. Land use adjusted into a pattern set by man should be utilized according to its capabilities. Optimum production and use of the land may be obtained by utilizing it for purposes to which it is best adapted. This is essentially a geographical problem in the final analysis and is manifested by a myriad of socio-economic factors that compose the gamut of land use implications. The author's interest in this area emanates from a field course in Geography and a number of trips through parts of this county. Field work was accomplished during the spring and summer of 1952 and constitutes the primary source of data for this thesis. The initials of the author appear where compilation of maps and graphs have been drawn from research and field data. All photographs have been taken by the author during his field work in the county.
The Chinese in Latin America, A Preliminary Geographical Survey with Special Reference to Cuba and Jamaica
(1956) Chang, Ching Chieh; McBryde, F. Webster; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
The present study concerns itself with the geographical origin, distribution, routes of migration and ports of embarkation of the Chinese in Latin America. It also purports to bring out the similarities and dissimilarities in their demographic composition, economic activities and some other aspects in different Latin American countries. The term "Latin America" is used to include all the European possessions in the area, and the term "Chinese" is used to include all those of Chinese parentage, but not those born to Chinese who intermarried with individuals of other races. Chinese immigration to Latin America on a large scale did not begin until the eighteen forties. Between 1847 and 1874, known as the coolie trade period, about one quarter of a million Chinese migrated to Latin America as "contract laborers". The great majority of them were "forced" immigrants, because they were kidnapped or decoyed by the coolie recruiters and did not migrate voluntarily. After 1874, Chinese immigration entered a new era. All the immigrants came voluntarily. But the good time of free Chinese immigration did not last very long. In or before the first quarter of the 20th century, most of the Latin American countries adopted laws to prohibit the entrance of Chinese. The Chinese immigrants were primarily from nine hsiens (or counties) in Kwangtung province immediately behind the port of Macao. Only those in Jamaica were not from this area, but exclusively from three hsiens in the same province north of Hongkong. At the present time, there are about 77 thousand Chinese in Latin America, and their distribution is highly localized. The localization of the geographical origin and the geographical distribution can be explained only in terms of the special type of Chinese emigration in general and the early history of the Chinese migration to Latin America in particular. Moreover, the Chinese are mainly concentrated in large cities. This is the result of their occupation. Almost all of them are engaged in commerce, and particularly in the grocery trade. Therefore, in places where their number is large, they are very influential in the grocery business. The Chinese population in almost all Latin American countries is characterized by two demographical anomalies: the great excess of males and the abnormally large number of old and middle-aged people. This is owing to the fact that, within the past one hundred years, the number of females among the immigrants has always been extremely small, and a large portion of the population still consists of immigrants who came in or before the nineteen twenties. Generally speaking, there has been no segregation against the Chinese along racial lines. Nevertheless, social contacts between Chinese and natives remain on a business basis and are purely ·functional. Racial consciousness still plays an important role among the Chinese, native-born as well as immigrants. Among the immigrants, it is also because most of them retain their Chinese nationality and want to go back to China eventually. Thus, in Latin America, the Chinese are not only racial minorities but also groups of aliens.
Land Use in Charles County
(1962) Langen, John S.; Van Royen, W.; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
The land use of Charles County does not basically differ from that in the past. Land in forest and land in farms are the two categories of land utilization. The great demand for tobacco on the overseas markets in the early days of the county's history, led to the introduction of this crop. Because of the favorable climate and soils, tobacco became soon the mainstay of the county's economy, a situation which still exists today. The purpose of the thesis was to determine which geographical factors and others accounted for the use of the land. In addition to field work, use was made of detailed statistical data. It was found, that the county could be divided into three sections. In the western section, land in forest was the dominating land use form. In the central section, land in forest and land in farms were about equal in areal extent, whereas in the eastern section, land in farms dominated. The reason was that soils in the western part became exhausted, and a shift to the eastern section took place. Landforms contributed much to the distribution of land in crops, especially for tobacco. Recently, a change in the use of the land is taking place. The encroachment of the Washington Metropolitan area, and the building of a major highway, connecting the North with the South, have induced farmers to sell their lands, which are converted into residential areas.
Colonia Incognita: The Formation of Chinatown, New York City, 1850-1890
(1975) Tom, Henry; Muller, Edward K.; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
The genesis of ethnic areas in cities is attributed to the process of residential concentration. For the Chinese experience in New York, however, the emergence of Chinatown occurred through the concentration of institutions. A rapid influx of Chinese into this northern industrial city followed by an occupational specialization in laundries – the coterminous place of work and residence – resulted in their widespread distribution. This spatial pattern prevented a residential concentration of the Chinese, who possessed a great cultural variance from the indigenous population. The migrational objective of returning to China with their accumulated earnings gave rise to the sojourning nature of Chinese migrants and its attendant detached status of migration without wives or families. These conditions generated a desire among the migrants to preserve their cultural identity, incurring a heavy reliance on things Chinese. In response, Chinatown had formed by 1880. Initially, a concentration of service and social institutions which fulfilled the socio-cultural needs of the dispersed Chinese population, Chinatown eventually became the basis for Chinese residential concentration.
Land Tenure, Property Ownership, and Home Mortgages in the Late Nineteenth Century: A Case Study of Baltimore's Germans
(1976) Vill, Martha J.; Groves, Paul A.; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
During the late nineteenth century the rapidly expanding urban population of the United States created an increased demand for housing. At the same time, mortgage money for the finance of home purchases was in short supply because of the availability of more lucrative investment opportunities elsewhere and because there were legal restrictions on the power of banks to lend money on real estate . Recent literature has emphasized the importance of property ownership among different components of the population, including immigrant groups. Little attention has been paid to the process of property acquisition or to the patterns of land tenure which resulted. An immigrant population, handicapped in numerous ways, was likely to have limited access to available mortgage financing, thereby limiting its ability to purchase property. Yet, the literature suggests that immigrants actively acquired property. This study examines some preliminary ideas about tenure patterns and home mortgages within immigrant residential areas, using a sample of Baltimore's Germans as a case study. The argument presented is that housing acquisition was facilitated by the activities of the immigrants themselves. In view of the restrictions on the supply of mortgage money, financing for property purchases had to come from sources independent of the city's major financial institutions, and the immigrants had to generate their own sources of capital. It was expected that tenants and landlords would have common national origins, another reflection of the immigrants' reliance on members of their own group for housing. Another expectation of the study was that Germans of different origins in Germany would exhibit different tenure patterns. Arguing that the term "German" was an imprecise indicator of national origins, and that the residential patterns of immigrants from different parts of Germany were distinct, it was expected that this diversity would also find expression in tenure patterns. The selection of the sample areas in the study was, therefore, conditioned by the need to isolate areas inhabited by Germans of diverse origins. Land tenure, property ownership, and relationships between landlords and tenants were analyzed. The hoped for differences in rates of property ownership did not materialize, and home ownership was not systematically related to age, income, or family employment. The findings do indicate, however, that home ownership was within the grasp of people with relatively low income. The mechanism which enabled home purchasers to obtain mortgages was the building and loan associations which were organized and directed by men whose origins, occupations, and residences reflected those of the associations' clientele. Thus, the hypothesis that immigrants generated their own mortgage funds was confirmed. The findings of the study concerning landlords and tenants further substantiate the argument that the provision of housing was accomplished by the immigrants themselves. Landlords' residences were close to the properties they rented, and there was a marked tendency for tenants to rent from landlords who shared their German origins.
The Evolution of Symbols on Nautical Charts Prior to 1800
(1979) Clawson, Mary G.; Wiedel, Joseph W.; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
This study attempts to determine the way in which symbols evolved on nautical charts, the identity of originators of these symbols, the spread in their use, and the forces involved in their continuing evolution. A twofold approach is utilized to resolve these questions. First a history of nautical charts prior to 1800 is presented and second, the actual examination of over 4200 nautical charts was carried out to discover and document their symbol content. A graphic summary of the symbols used on these charts is presented along with an analysis of the data gathered in 1 ight of the history of nautical cartography. The evolution of the symbols on nautical charts was found to be closely aligned with one of the three types of symbols described by Dreyfuss (1972): arbitrary, abstract or representational. The arbitrary symbols examined in this study clearly went through an evolutionary process, whereas the abstract and representational symbols remained virtually static throughout the period. The originators of the symbols are given when identifiable and the spread and evolution of the symbols is discussed. From this study it can be concluded that this type of research is most valuable in discovering the evolution of symbols on nautical charts and that the graphic summary could be considered a standard for evaluating the evolution and use of symbols on nautical charts prior to 1800.
Washington, D.C.'s Streetcar Suburbs: A Comparative Analysis of Brookland and Brightwood, 1870-1900
(1979) Prince, Thomas Eugene; Groves, Paul
The evolution of public transportation systems in the large American cities of the late nineteenth century culminated in the innovation of the streetcar. Such transportation changes affected urban structure and by the last quarter of the century had produced a distinctive residential area, the streetcar suburb. Washington, D.C. had a number of such suburbs, some the result of subdivision development associated with the extension of streetcar lines to link existing village suburbs to the downtown core, others the product of concurrent residential subdivision and streetcar development. Such suburbs were predominantly middle-class, white, residential areas. An examination of two Washington, D.C. suburbs: Brightwood and Brookland, indicated distinct physical, social, economic, and demographic structures in these village suburbs in the early 1880's. After the subsequent introduction of streetcar links to downtown Washington--an employment core characterized by much white-collar government employment--the two suburbs became increasingly similar in terms of the chosen measurements. By the end of the century, there was little in their structures to indicate the very different paths they had taken to the same end.
Washington, D.C. and the Growth of Its Early Suburbs : 1860-1920
(1980) Levy, Anneli Moucka; Groves, Paul A.; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
During the nineteenth century, the North American city greatly changed in size and internal structure. With the introduction of mass transportation, large scale suburbanization took place as one aspect of this change. Members of the evolving middle class not only wished to escape the pollution and congestion of the urban core, but also believed strongly in a 'rural ideal,' translated into a 'suburban ideal.' Urban changes and suburban growth were especially pronounced in industrial cities, and descriptions of conditions in these cities identify the accepted model of the spatial configuration of the metropolis existed in 1920. Examination of the growth of Washington D. C. between the Civil War and World War I indicates that the city shared few of the characteristics of the accepted urban model. Nevertheless, it exhibited distinct suburban movement connected with three major transport modes, including the steam railroad. The belief in the 'suburban ideal' was broadly based in Washington and therefore much variation was found among the city's suburban communities, even among those associated with the same transportation mode. Furthermore, in contrast to the suburban model, conditions in the suburban areas often did not compare favorably with those in the city. Even so, the suburbanization process accelerated from small beginnings, so that by 1920 the city displayed the local variant of the typical star-shaped pattern.
Historical Shoreline Changes in Response to Environmental Conditions in West Delaware Bay
(1990) French, Gregory T.; Leatherman, Stephen
This study quantified historical changes in the coastline of the west shore of Delaware Bay. Shoreline changes were measured through the compilation of historical maps and photographs utilizing the Metric Mapping technique. These changes were correlated with various environmental conditions and with human influences. The results portray a 135 year pattern of overall erosion, with long-term rates averaging -4.5 ftjyr, which is considerably greater than the u.s. Atlantic coast average. Coastal engineering (e.g., groins, jetties and beach nourishment) were locally effective in reducing erosion rates and in some cases promoting limited accretion. Perhaps more importantly, there were few associated negative effects alongshore suggesting that various forms of coastal engineering can be effective in a low-energy environment, even when done in a somewhat unorganized fashion. A correlation was found between erosion rates and underlying Pleistocene morphology. Where pre-Holocene sediments were exposed in the nearshore, erosion rates were lower. However, erosion rates were substantially higher along marshy shorelines. This erosion is not continuous either spatially or temporally, but instead is largely storm-driven. Periods of relative quiescence corresponded with lowered rates of average annual shoreline recession. With the exception of the northernmost marshy areas, severe erosion occurs along all shorelines, regardless of morphology, in response to major coastal storms.
Island Land Loss in the Chesapeake Bay: A Quantitative and Process Analysis
(1992) Wray, Rachel Donham; Leatherman, Stephen P.; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
The rates and processes of land loss were studied for seven islands in the Chesapeake Bay: Barren, Bloodsworth, Hooper, James, Poplar, Smith and South Marsh Islands. Rates and patterns of land loss were quantified for the years 1848 to 1987 with the Metric Mapping technique which utilizes digitized data from historical maps and vertical aerial photographs. Processes of land loss were determined through field surveys and correlated with environmental factors. Two distinct island types were identified which exhibited different, long-term patterns of land loss. Small, upland islands, termed the Northern Group, showed rapid land loss along the main stem of the Bay primarily due to wave action driven by the predominant westerly winds. Land loss appeared to accelerate during periods of high storm frequency. The long-term averaged land loss rate for Northern Group islands is 1.9 ha/yr. The averaged erosion rate on the western side of the islands is 4.9 m/yr, compared to 0.68 m/yr on the eastern side of the islands. In contrast, the large, marshy islands of the Southern Group experienced uniform marsh edge erosion and interior marsh degradation. The Southern Group islands lost land at an averaged rate of 5. 6 ha/yr, with an averaged rate of marsh edge erosion of 1.2 m/yr. Land loss appeared to be weakly correlated to storm frequency. Interior marsh loss was not quantified for this study, however, so this study provides an underestimation of total land loss of coastal wetlands.
RECONSTRUCTION OF A DOWNTOWN: THE AFTERMATH OF THE GREAT BALTIMORE FIRE OF 1904
(1993) Wingo, Amanda Jean; Groves, Paul; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
Reconstruction following a major disaster has farreaching impacts which can alter the functioning of a city. Understanding this process is therefore vital. The results of such a study add to the small body of literature on reconstruction following disaster and thus provides additional testing of the findings of Bowden(l967), the critical piece of literature on reconstruction to date. Specifically, this thesis considers the process of reconstruction by looking at the structural and spatial changes predicted by one catastrophic event. Using both Sanborn Atlases and Baltimore Business Directories between 1902 and 1914, the Central Business District (CBD) is examined through the analysis of concentration, sequencing, and persistence processes. More important, however, is the extent to which these processes impact the spatial characteristics of establishments within the Burnt District over a specific period of time (1902- --- ·--·-- 1914). A significant finding indicates that in the pre- and post-fire period Baltimore maintains a high degree of consistency within the Burnt District. However 1 the vertical dimension of Baltimore changes drastically from 1902 to 1914 allowing an increase in the availability of space explained by the vertical growth of buildings. The sequence of return of the "building block" establishments occurred within a surprising two years following the fire. Several defining situations fix or anchor establishments to their locations 1 which act to mitigate the variations in land-use patterns over time. The findings of this study provide a spatial view of the functional districts which play an important role in the life of the CBD of Baltimore.
Calculation of the Angular Radiance Distribution for a Coupled Atmosphere and Canopy
(Institute of Electrical and Electronics Engineers, 1993-03) Liang, Shunlin; Strahler, Alan H.
The radiative transfer equations for a coupled atmosphere and canopy are solved numerically by an improved Gause-Seidel iteration algorithm. The radiation field is decomposed into three components: unscattered sunlight, single scattering, and multiple scattering radiance for which the corresponding equations and boundary conditions are set up and their analytical or iterational solutions are explicitly derived. The classic Guass-Seidel algorithm has been widely applied in atomospheric research. This is its first application for calculating the multiple scattering radiance of a coupled atmosphere and canopy. This algorithm enables us to obtain the internal radiation field as well as radiances at boundaries. Any form of bidirectional reflectance distribution function (BRDF) as a boundary condition can be easily incorporated into the iteration procedure. The hotspot effect of the canopy is accommodated by means of the modification of the extiniction coefficients of upward single scattering radiation and unscatteered sunlight using the formulation of Nilson and Kuusk. To reduce the computation for the case of large optical thickness, an improved iteration formula is derived to speed convergence. The upwelling radiances have been evaluated for different atmospheric conditions, leaf area index (LAI), leaf angle distribution (LAD), leaf size and so on. The formulation presented in this paper is also well suited to analyze the relative magnitude of multiple scattering radiance and single scattering radiance in both the visible and near infrared regions.
An Analytic BRDF Model of Canopy Radiative Transfer and Its Inversion
(Institute of Electrical and Electronics Engineers, 1993-09) Liang, Shunlin; Strahler, Alan H.
Radiative transfer modeling of the bidirectional reflectance distribution function (BRDF) of leaf canopies is a powerful tool to relate multiangle remotely sensed data to biophysical parameters of the leaf canopy and to retrieve such parameters from multiangle imagery. However, the approximate approaches for multiple scattering that are used in the inversion of existing models are quite limited, and the sky radiance frequently is simply treated as isotropic. This paper presents an analytical model based on a rigorous canopy radiative transfer equation in which the multiple-scattering component is approximated by asymptotic theory and the single-scattering calculation, which requires numerical integration to properly accommodate the hotspot effect, is also simplified. Because the model is sensitive to angular variation in sky radiance, we further provide an accompanying new formulation for directional radiance in which the unscattered solar radiance and single-scattering radiance are calculated exactly, and multiple-scattering is approximated by the well-known two-stream Dirac delta function approach. A series of validations against exact calculations indicates that both models are quite accurate, especially when the viewing angle is smaller than 55 degrees. The Powell algorithm is then used to retrieve biophysical parameters from multiangle observations based on both the canopy and the sky radiance distribution models. The results using the soybean data of Ranson et al. to recover four of nine soybean biophysical parameters indicate that inversion of the present canopy model retrieves leaf area index well. Leaf angle distribution was not retrieved as accurately for the same dataset, perhaps because these measurements do not describe the hotspot well. Further experiments are required to explore the applicability of this canopy model.
THE USE OF NARROW SPECTRAL BANDS FOR IMPROVING REMOTE SENSING ESTIMATIONS OF FRACTIONALLY ABSORBED PHOTOSYNTHETICALLY ACTIVE RADIATION
(1994) Kim, Moon Sung; Townshend, John R.G.; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
Most remote sensing estimations of vegetation variables such as leaf area index (LAI), absorbed photosynthetically active radiation (Apar,), and primary production are made using broad band sensors with a bandwidth of approximately 100 nm. However, high resolution spectrometers are available and have not been fully exploited for the purpose of improving estimates of vegetation variables. The study was directed to investigate the use of high spectral resolution spectroscopy for remote sensing estimates of f apar in vegetation canopies in the presence of nonphotosynthetic background materials such as soil and leaf litter. A high spectral resolution measure defined as the chlorophyll absorption ratio index (CARI) was developed for minimizing the effects of nonphotosynthetic materials in the remote estimates of f apar CARI utilizes three bands at 550, 670, and 700 nm with bandwidth of 10 nm. Simulated canopy reflectance of a range of leaf area index (LAI) were generated with the SAIL model using measurements of 42 different soil types as canopy background. CARI calculated from the simulated canopy reflectance was compared with the broad band vegetation indices such as normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), and simple ratio (SR). CARI reduced the effect of nonphotosynthetic background materials in the assessment of vegetation canopy f apar more effectively than broad band vegetation indices.
An Optimization Algorithm for Separating Land Surface Temperature and Emissivity from Multispectral Thermal Infrared Imagery
(Institute of Electrical and Electronics Engineers, 2001-02) Liang, Shunlin
Land surface temperature (LST) and emissivity are important components of land surface modeling and applications. The only practical means of obtaining LST at spatial and temporal resolutions appropriate for most modeling applications is through remote sensing. While the popular split-window method has been widely used to estimate LST, it requires known emissivity values. Multispectral thermal infrared imagery provides us with an excellent opportunity to estimate both LST and emissivity simultaneously, but the difficulty is that a single multispectral thermal measurement with bands presents equations in + 1 unknowns ( spectral emissivities and LST). In this study, we developed a general algorithm that can separate land surface emissivity and LST from any multispectral thermal imagery, such as moderate-resolution imaging spectroradiometer (MODIS) and advanced spaceborne thermal emission and reflection radiometer (ASTER). The central idea was to establish empirical constraints, and regularization methods were used to estimate both emissivity and LST through an optimization algorithm. It allows us to incorporate any prior knowledge in a formal way. The numerical experiments showed that this algorithm is very effective (more than 43.4% inversion results differed from the actual LST within 0.5 , 70.2% within 1 and 84% within 1.5 ), although improvements are still needed.
Atmospheric Correction of Landsat ETM+ Land Surface Imagery—Part I: Methods
(Institute of Electrical and Electronics Engineers, 2001-11) Liang, Shunlin; Fang, Hongliang; Chen, Mingzhen
To extract quantitative information from the Enhanced Thematic Mapper-Plus (ETM+) imagery accurately, atmospheric correction is a necessary step. After reviewing historical development of atmospheric correction of Landsat thematic mapper (TM) imagery, we present a new algorithm that can effectively estimate the spatial distribution of atmospheric aerosols and retrieve surface reflectance from ETM+ imagery under general atmospheric and surface conditions. This algorithm is therefore suitable for operational applications. A new formula that accounts for adjacency effects is also presented. Several examples are given to demonstrate that this new algorithm works very well under a variety of atmospheric and surface conditions. The companion paper will validate this method using ground measurements, and illustrate the improvements of several applications due to atmospheric correction.
Atmospheric Correction of Landsat ETM+ Land Surface Imagery: II. Validation and Applications
(Institute of Electrical and Electronics Engineers, 2002) Liang, Shunlin; Morisette, Jeffrey T.; Fang, Hongliang; Chen, Mingzhen; Shuey, Chad J.; Daughtry, Craig S. T.; Walthall, Charles L.
This is the second paper of the series on atmospheric correction of ETM+ land surface imagery. In the first paper, a new algorithm that corrects heterogeneous aerosol scattering and surface adjacency effects was presented. In this study, our objectives are to 1) evaluate the accuracy of this new atmospheric correction algorithm using ground radiometric measurements; 2) apply this algorithm to correct MODIS and SeaWiFS imagery; and 3) demonstrate how much atmospheric correction of ETM+ imagery can improve land cover classification, change detection, and broadband albedo calculations. Validation results indicate that this new algorithm can retrieve surface reflectance from ETM+ imagery accurately. All experimental cases demonstrate that this algorithm can be used for correcting both MODIS and SeaWiFS imagery. Although more tests and validation exercises are needed, it has been proven promising to correct different multispectral imagery operationally. We have also demonstrated that atmospheric correction does matter.
A Direct Algorithm for Estimating Land Surface Broadband Albedos From MODIS Imagery
(Institute of Electrical and Electronics Engineers, 2003-01) Liang, Shunlin
Land surface albedo is a critical variable needed in land surface modeling. The conventional methods for estimating broadband albedos rely on a series of steps in the processing chain, including atmospheric correction, surface angular modeling, and narrowband-to-broadband albedo conversions. Unfortunately, errors associated with each procedure may be accumulated and significantly impact the accuracy of the final albedo products. In an earlier study, we developed a new direct procedure that links the top-of-atmosphere spectral albedos with land surface broadband albedos without performing atmospheric correction and other processes. In this paper, this method is further improved in several aspects and implemented using actual Moderate Resolution Imaging Spectroradiometer (MODIS) imagery. Several case studies indicated that this new method can predict land surface broadband albedos very accurately and eliminate aerosol effects effectively. It is very promising for global applications and is particularly suitable for nonvegetated land surfaces. Note that a Lambertian surface has been assumed in the radiative transfer simulation in this paper as a first-order approximation; this assumption can be easily removed as long as a global bidirectional reflectance distribution function climatology is available,
Consistency of MODIS surface bidirectional reflectance distribution function and albedo retrievals: 2. Validation
(American Geophysical Union, 2003-03-08) Liang, Shunlin; Lucht, Wolfgang; Jin, Yufang; Schaaf, Crystal B.; Woodcock, Curtis E.; Gao, Feng; Li, Xiaowen
The evaluation of the first available satellite-based global albedo product at 1-km resolution is essential for its application in climate studies. We evaluate the accuracy of the Moderate-Resolution Imaging Spectroradiometer (MODIS) albedo product using available field measurements at Surface Radiation Budget Network (SURFRAD) and Cloud and Radiation Testbed–Southern Great Plains (CART/SGP) stations and examine the consistency between the MODIS surface albedos and the Clouds and Earth’s Radiant Energy System (CERES) top-of-the-atmosphere albedos as well as historical global albedos from advanced very high resolution radiometer (AVHRR) and Earth Radiation Budget Experiment (ERBE) observations. A comparison with the field measurements shows that the MODIS surface albedo generally meets an absolute accuracy requirement of 0.02 for our study sites during April–September 2001, with the root mean square errors less than 0.018. Larger differences appear in the winter season probably due to the increased heterogeneity of surface reflectivity in the presence of snow. To examine the effect of spatial heterogeneity on the validation of the MODIS albedos using fine resolution field measurements, we derive an intermediate albedo product from four Landsat Enhanced Thematic Mapper Plus (ETM+) images at 30-m spatial resolution as a surrogate for the distributed field measurements. The surface albedo is relatively homogeneous over the study stations in growing seasons, and therefore the validation during April–September is supported. A case study over three SURFRAD stations reveals that the MODIS bidirectional reflectance distribution function model is able to capture the solar zenith angle dependence of surface albedo as shown by the field measurements. We also find that the MODIS surface shortwave albedo is consistent with the contemporary and collocated CERES top-of atmosphere albedos derived directly from broadband observations. The MODIS albedo is also well correlated with historical surface albedos derived from AVHRR and ERBE observations, and a high bias of 0.016 and a low bias of 0.034 compared to those of the latter albedos are reasonable considering the differences in instruments and retrieval algorithms as well as environmental changes.
Consistency of MODIS surface BRDF/Albedo retrievals 1. Algorithm performance
(American Geophysical Union, 2003-03-08) Liang, Shunlin; Jin, Yufang; Lucht, Wolfgang; Schaaf, Crystal B.; Gao, Feng; Li, Xiaowen; Strahler, Alan H.
The first consistent year (November 2000 to November 2001) of global albedo product was produced at 1-km resolution every 16 days from the observations of the Moderate- Resolution Imaging Spectroradiometer (MODIS) instrument aboard NASA’s Terra spacecraft.We evaluated the quality of the operational albedo retrievals in two ways: (1) by examining the algorithm performance using the product quality assurance (QA) fields (this paper) and (2) by comparing retrieved albedos with those observed at ground stations and by other satellite instruments (in a companion paper). The internal diagnostics of the retrieval algorithm adequately reflect the goodness of the model fit and the random noise amplification in the retrieved albedo. Global QA statistics show that the RossThick- LiSparse-Reciprocal model fits the atmospherically corrected surface reflectances very well, and the random noise amplification factors for white sky albedo and reflectance are generally less than 1.0. Cloud obscuration is the main reason for the activation of the backup magnitude retrieval algorithm. Over the 60°S to 60°N latitude band, 50% of the land pixels acquire more than six clear looks during 14–29 September 2001, and only 5% of these pixels are inverted with the backup algorithm. The latitude dependence and temporal distribution of the QA fields further demonstrate that the retrieval status mainly follows the pattern of angular sampling determined by cloud climatology and the instrument/orbit characteristics. A case study over the west coast of the United States shows that white sky shortwave albedos retrieved from magnitude inversions agree on average with those from full inversions to within 0.033 in reflectance units and have a slightly lower bias ranging from 0.014 to 0.023. We also explored the effect of residual cloud and aerosol contamination in the atmospherically corrected surface reflectance inputs in another case study over southern Africa. The quality assurance procedure of the operational MODIS bidirectional reflectance distribution function and albedo algorithm compensates for some of these residual effects and improves the albedo retrieval results by an order of 0.005 (10%) in the visible for more than 12% of pixels.