Hyperspectral imaging (HSI) electro-optical sensors, with their hundreds of contiguous spectral b... more Hyperspectral imaging (HSI) electro-optical sensors, with their hundreds of contiguous spectral bands, are a rich data source useful in a variety of applications. Numerous examples have demonstrated their potential. Understanding the characteristics of HSI data is important not only for algorithm design and assessment, but also for accurate modeling in a performance prediction context. Initial results are presented from an investigation exploring the applicability of characterizing the data with the first and second spectral statistical moments.
A critical assessment of the data archive system at Purdue University in West Lafayette, Indiana,... more A critical assessment of the data archive system at Purdue University in West Lafayette, Indiana, USA, is detailed with specific reference to those aspects that may be appropriate within a sustainable development context. The Purdue Terrestrial Observatory (PTO) benefits from an archive of satellite data, amassed over the past forty years by the Laboratory for Applications of Remote Sensing (LARS), real-time multi-sensor satellite groundstations, a recent five petabyte upgrade to the storage system, an array of available Linux clusters and supercomputers for rapid data analysis, fusion and mining, a state-of-the-science data Visualization and Perceptualization Center, real-time nation-wide access to NEXRAD/WSR-88D Doppler Radar installations, an elaborate network of high bandwidth connectivity to other academic research centers and federal government laboratories throughout the United States, high-resolution weather forecast output from a variety of environmental models, internation...
This study is a result of a project titled ''Useful to Usable (U2U): Transforming Climate Variabi... more This study is a result of a project titled ''Useful to Usable (U2U): Transforming Climate Variability and Change Information for Cereal Crop Producers". This paper responds to the project goal to improve farm resiliency and profitability in the U.S. Corn Belt region by transforming existing meteorological dataset into usable knowledge and tools for the agricultural community. A high-resolution agro-climatic dataset that covers the U.S. Corn Belt was built for the U2U project based on a Land Data Assimilation System (LDAS) framework. This data referred to as the Purdue Agro-climatic (PAC) dataset is a gridded, continuous dataset suitable for agroclimatic and crop model studies over the U.S. Corn Belt. The dataset was created at 4 km, subdaily spatiotemporal resolution and covers the period of 1981-2014. The dataset includes a range of variables such as daily maximum/minimum temperature, solar radiation, rainfall, evapotranspiration (ET), multilevel soil moisture and soil temperatures. The data were compared to field measurements from Ameriflux and the Soil Climate Analysis Network (SCAN), and with coarser but widely used atmospheric regional reanalysis data products. Validations indicate an overall good agreement between this dataset and field measurements. The agreement is particularly high for radiation and temperature parameters and lesser for rainfall and soil moisture data. Despite the differences with observations, the data show improvements over the coarser resolution products and other available models and thus highlights the value of the dataset for agroclimatic and crop model studies. This high-resolution dataset is available to the wider community, and can fill gaps in observed data records and increase accessibility for the agricultural sector, and for conducting variety of if-then assessments.
2006 IEEE International Symposium on Geoscience and Remote Sensing, 2006
Specialized software systems have played a crucial role throughout the twenty-five year course of... more Specialized software systems have played a crucial role throughout the twenty-five year course of the development of the new technology of imaging spectroscopy, or hyperspectral remote sensing. By their very nature, hyperspectral data place unique and demanding requirements on the computer software used to visualize, analyze, process and interpret them. Often described as a marriage of the two technologies of reflectance spectroscopy and airborne/spaceborne remote sensing, imaging spectroscopy, in fact, produces data sets with unique qualities, unlike previous remote sensing or spectrometer data. Because of these unique spatial and spectral properties hyperspectral data are not readily processed or exploited with legacy software systems inherited from either of the two parent fields of study. This paper provides brief reviews of seven important software systems developed specifically for imaging spectroscopy.
E-4. Example of 3-dimensional surface type plot using 3-D Graphics Compatibility System Software.... more E-4. Example of 3-dimensional surface type plot using 3-D Graphics Compatibility System Software. This plot represents the joint density function for two channels and six classes in a LARSYS statistics deck for Skylab data .
The spectral reflective response of plants, soils, and rocks may contain information concentrated... more The spectral reflective response of plants, soils, and rocks may contain information concentrated in relatively narrow spectral regions defined by the light absorption properties of the constituent atoms and molecules. The hope exists that such information will be of value in remote sensing in discriminating information classes, in identifying growth stages and stress conditions in crops, and in delineating the
MyGeoHub is a science gateway for researchers working with geospatial data. Based on the HUBzero ... more MyGeoHub is a science gateway for researchers working with geospatial data. Based on the HUBzero cyberinfrastructure framework, it provides general-purpose software modules enabling geospatial data management, processing and visualization. Termed "GABBs" (Geospatial Data Analysis Building Blocks), these modules can be leveraged to build geospatial data driven tools with minimal programming and construct dynamic workflows chaining both local and remote tools and data sources. We will present examples of such end-to-end workflows demonstrating the underlying software building blocks that have also found use beyond the MyGeoHub gateway in other science domains.
Proceedings of the Practice and Experience in Advanced Research Computing 2017 on Sustainability, Success and Impact, 2017
Modern cyberinfrastructures typically involve tightly integrated compute, storage and web applica... more Modern cyberinfrastructures typically involve tightly integrated compute, storage and web application resources. They also form the basis of science gateways, which add their own science-specific processing or visualization capabilities. While some science gateways are intended as the central resource provider for a certain scientific community, others provide generic capabilities that are intended for further customization at each installation site. However, replicating their setup is a non-trivial task often involving specific operating system, software package and configuration choices while also requiring allocation of the actual physical computing resources. Cloud computing provides an attractive alternative, simplifying resource provision and enabling reliable replication. We describe our ongoing efforts to cloud-enable a geospatial science gateway hosting general-purpose software building blocks termed GABBs, that provide geospatial data management, analysis, visualization and processing capabilities. We describe the various compute and storage resources and software underlying these building blocks and our automation of the deployment, software installation and configuration of this science gateway on the Amazon Web Services (AWS) cloud platform. Some of the challenges that were encountered and resolved during this cloud-enabling process are also described.
Science gateways have gained wide adoption in recent years as an effective platform for a lower b... more Science gateways have gained wide adoption in recent years as an effective platform for a lower barrier entry to computational resources, research collaboration, dissemination of scientific data, applications and publications, online education, and community engagement. Although multiple portal frameworks and middleware toolkits exist to facilitate the development of a science gateway, the task of bringing data and tools online into a science gateway environment is still daunting for domain science users. In this paper, we describe GABBs, a National Science Foundation funded project that aims to reduce this obstacle by delivering reusable software building blocks for geospatial data management and analysis based on the HUBzero portal platform. The main components of GABBs include a geospatial data management system named iData, libraries for easy creation of geospatial data analysis tools hosted in the gateway, GeoBuilder for creating GIS-enabled data exploration tools without progr...
Science gateways are an integral component of modern collaborative research. They find widespread... more Science gateways are an integral component of modern collaborative research. They find widespread adoption by research groups to share data, code and tools both amongst collaborators on a project and the broader community. However, not unlike research groups, gateways too, face the vagaries of research funding often resulting in a bleak outlook for their maintenance beyond the original project's conclusion. We present a sustainability model based on the HUBzero cyberinfrastructure platform that enables multiple research projects to share a single science gateway allowing for their maintenance even after the original funding source has run out. This model brings with it certain other advantages as well; general improvements to the gateway apply to all hosted projects, similar requirements across projects can often be abstracted into new general purpose capabilities for the gateway which feed back into all hosted projects. Such newly developed capabilities can also foster additional research aiding in new funding proposals that can revitalize and jumpstart hosted dormant projects. We describe a specific instance of a HUBzero science gateway, MyGeoHub, that successfully employs this sustainability model to host several geospatial research
This paper describes the use of cyberinfrastructure to create interactive applications as part of... more This paper describes the use of cyberinfrastructure to create interactive applications as part of the Useful to Usable (U2U) project. These applications transform historical climate data, knowledge, and models into decision support tools for end users such as crop farmers, university Extension educators, and other agricultural advisors. In creating a cyberinfrastructure to support the U2U project, four major challenges have been addressed: designing and developing highly usable web applications with frequent feedback, establishing a software engineering environment to support iterative development, integrating and synthesizing historical and current datasets from a variety of sources (local vs. remote, different access methods, and formats), and supporting project collaboration needs of data and document sharing, project management, and public outreach. The overall goals of the cyberinfrastructure and its architecture design are described. Methods for data retrieval and synthesis, as well as the various software components utilized are discussed. The development and integration of tools into the collaborative HUBzero framework are highlighted, including the use of HUBzero's core features to share ideas, algorithms, and results. A highly iterative development process that includes feedback from experts and end-users to feed requirement definition, design and application updates are also examined.
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
for Applications of Remote Sensing (LARS), was a primary innovator in the field of digital image ... more for Applications of Remote Sensing (LARS), was a primary innovator in the field of digital image analysis and remote sensing of the environment. He and his LARS colleagues, along with a select few other researchers at institutions including the
The author has identified the following significant results. The LACIE field measurement data wer... more The author has identified the following significant results. The LACIE field measurement data were radiometrically calibrated. Calibration enabled valid comparisons of measurements from different dates, sensors, and/or locations. Thermal band canopy results included: (1) Wind velocity had a significant influence on the overhead radiance temperature and the effect was quantized. Biomass and soil temperatures, temperature gradient, and canopy geometry were altered. (2) Temperature gradient was a function of wind velocity. (3) Temperature gradient of the wheat canopy was relatively constant during the day. (4) The laser technique provided good quality geometric characterization.
Photogrammetric Engineering and Remote Sensing, 1986
An experiment is described that examines the effects of solar zenith angle and background reflect... more An experiment is described that examines the effects of solar zenith angle and background reflectance on the composite scene reflectance of small balsam fir (Abies balsamea (L.) Mill.) arranged in different densities. In this study, the shape, density, and, consequently, the needle area index and phytomass of the canopies, as well as the background reflectance, were controlled. The effects of sun angle, view angle, and background reflectance on the multispectral response of small balsam fir trees were significant. Regression models relating spectral vegetation indices (i.e., normalized difference (ND) and greenness (GR) to phytomass) showed very poor relationships for balsam fir canopies with a grass background. However, strong linear relationships were found for ND and GR with phytomass for a background that simulated the reflectance of snow. Changing solar zenith angle significantly affected the models relating ND to phytomass for the snow background, but was not significant in th...
A leaf begins to senesce as soon as it is removed from the plant and changes in metabolic process... more A leaf begins to senesce as soon as it is removed from the plant and changes in metabolic processes and spectral properties are inevitable. If senescence can be delayed for several days without significant changes in spectral properties, then samples of leaves at remote test sites could be prepared and shipped to laboratories which have the equipment to measure spectral properties. The objective of this study was to determine the changes in spectral properties of detached leaves. Leaves from red birch (Betula nigra L.) and red pine (Pinus resinosa Ait.) were immersed for 5 minutes in water or 0.001 M benzylaminopurine (BAP) and stored in plastic bags in the dark at either 5° or 25° C. Total directional-hemispherical reflectance and transmittance of the adaxial surface of birch leaves were measured over the 400 to 1100 nm wavelength region with a spectroradiometer and integrating sphere (LICOR LI-1800). Pine needles were taped together and reflectance of the mat of needles was measured. Spectral properties changed less than 5% of initial values during the first week when leaves were stored at 5° C. Storage at 25° C promoted rapid senescence and large changes in spectral properties. BAP delayed, but did not stop, senescence at 25° C. Low temperature was more effective than BAP in delaying senescence. It appears possible to store leaves at low temperatures in plastic bags in the dark for several days without significantly altering the spectral properties in the 400 to 1100 nm wavelength region.
Percent of total variation in reflectances, greenness and brightness accounted for by soil moistu... more Percent of total variation in reflectances, greenness and brightness accounted for by soil moisture level and significant agronomic factors and interactions.. .. . A-31 Mean agronomic characteristics of spring wheat canopies by soil moisture level and planting date. •. .. .... .. . A-32 Percent correct classification of spring wheat, fallow, and pasture using unitemporal information (Williams Co.
A-3.7. Seasonal changes in four spectral variables and percent soil cover for two row widths in 1... more A-3.7. Seasonal changes in four spectral variables and percent soil cover for two row widths in 1979 for the June 15 planting date. Development stages are indicated for each Page 38 observation date (Russell silt loam). • • • • 39 A-3.8. Seasonal changes in four spectral variables and percent. soil cover for three planting dates in 1979 for 75 cm wide rows. Development stages (Fehr and Caviness, 1977) are indicated for each observation date. Arrows indicate development stages that are unique for that planting date (Russell silt
Hyperspectral imaging (HSI) electro-optical sensors, with their hundreds of contiguous spectral b... more Hyperspectral imaging (HSI) electro-optical sensors, with their hundreds of contiguous spectral bands, are a rich data source useful in a variety of applications. Numerous examples have demonstrated their potential. Understanding the characteristics of HSI data is important not only for algorithm design and assessment, but also for accurate modeling in a performance prediction context. Initial results are presented from an investigation exploring the applicability of characterizing the data with the first and second spectral statistical moments.
A critical assessment of the data archive system at Purdue University in West Lafayette, Indiana,... more A critical assessment of the data archive system at Purdue University in West Lafayette, Indiana, USA, is detailed with specific reference to those aspects that may be appropriate within a sustainable development context. The Purdue Terrestrial Observatory (PTO) benefits from an archive of satellite data, amassed over the past forty years by the Laboratory for Applications of Remote Sensing (LARS), real-time multi-sensor satellite groundstations, a recent five petabyte upgrade to the storage system, an array of available Linux clusters and supercomputers for rapid data analysis, fusion and mining, a state-of-the-science data Visualization and Perceptualization Center, real-time nation-wide access to NEXRAD/WSR-88D Doppler Radar installations, an elaborate network of high bandwidth connectivity to other academic research centers and federal government laboratories throughout the United States, high-resolution weather forecast output from a variety of environmental models, internation...
This study is a result of a project titled ''Useful to Usable (U2U): Transforming Climate Variabi... more This study is a result of a project titled ''Useful to Usable (U2U): Transforming Climate Variability and Change Information for Cereal Crop Producers". This paper responds to the project goal to improve farm resiliency and profitability in the U.S. Corn Belt region by transforming existing meteorological dataset into usable knowledge and tools for the agricultural community. A high-resolution agro-climatic dataset that covers the U.S. Corn Belt was built for the U2U project based on a Land Data Assimilation System (LDAS) framework. This data referred to as the Purdue Agro-climatic (PAC) dataset is a gridded, continuous dataset suitable for agroclimatic and crop model studies over the U.S. Corn Belt. The dataset was created at 4 km, subdaily spatiotemporal resolution and covers the period of 1981-2014. The dataset includes a range of variables such as daily maximum/minimum temperature, solar radiation, rainfall, evapotranspiration (ET), multilevel soil moisture and soil temperatures. The data were compared to field measurements from Ameriflux and the Soil Climate Analysis Network (SCAN), and with coarser but widely used atmospheric regional reanalysis data products. Validations indicate an overall good agreement between this dataset and field measurements. The agreement is particularly high for radiation and temperature parameters and lesser for rainfall and soil moisture data. Despite the differences with observations, the data show improvements over the coarser resolution products and other available models and thus highlights the value of the dataset for agroclimatic and crop model studies. This high-resolution dataset is available to the wider community, and can fill gaps in observed data records and increase accessibility for the agricultural sector, and for conducting variety of if-then assessments.
2006 IEEE International Symposium on Geoscience and Remote Sensing, 2006
Specialized software systems have played a crucial role throughout the twenty-five year course of... more Specialized software systems have played a crucial role throughout the twenty-five year course of the development of the new technology of imaging spectroscopy, or hyperspectral remote sensing. By their very nature, hyperspectral data place unique and demanding requirements on the computer software used to visualize, analyze, process and interpret them. Often described as a marriage of the two technologies of reflectance spectroscopy and airborne/spaceborne remote sensing, imaging spectroscopy, in fact, produces data sets with unique qualities, unlike previous remote sensing or spectrometer data. Because of these unique spatial and spectral properties hyperspectral data are not readily processed or exploited with legacy software systems inherited from either of the two parent fields of study. This paper provides brief reviews of seven important software systems developed specifically for imaging spectroscopy.
E-4. Example of 3-dimensional surface type plot using 3-D Graphics Compatibility System Software.... more E-4. Example of 3-dimensional surface type plot using 3-D Graphics Compatibility System Software. This plot represents the joint density function for two channels and six classes in a LARSYS statistics deck for Skylab data .
The spectral reflective response of plants, soils, and rocks may contain information concentrated... more The spectral reflective response of plants, soils, and rocks may contain information concentrated in relatively narrow spectral regions defined by the light absorption properties of the constituent atoms and molecules. The hope exists that such information will be of value in remote sensing in discriminating information classes, in identifying growth stages and stress conditions in crops, and in delineating the
MyGeoHub is a science gateway for researchers working with geospatial data. Based on the HUBzero ... more MyGeoHub is a science gateway for researchers working with geospatial data. Based on the HUBzero cyberinfrastructure framework, it provides general-purpose software modules enabling geospatial data management, processing and visualization. Termed "GABBs" (Geospatial Data Analysis Building Blocks), these modules can be leveraged to build geospatial data driven tools with minimal programming and construct dynamic workflows chaining both local and remote tools and data sources. We will present examples of such end-to-end workflows demonstrating the underlying software building blocks that have also found use beyond the MyGeoHub gateway in other science domains.
Proceedings of the Practice and Experience in Advanced Research Computing 2017 on Sustainability, Success and Impact, 2017
Modern cyberinfrastructures typically involve tightly integrated compute, storage and web applica... more Modern cyberinfrastructures typically involve tightly integrated compute, storage and web application resources. They also form the basis of science gateways, which add their own science-specific processing or visualization capabilities. While some science gateways are intended as the central resource provider for a certain scientific community, others provide generic capabilities that are intended for further customization at each installation site. However, replicating their setup is a non-trivial task often involving specific operating system, software package and configuration choices while also requiring allocation of the actual physical computing resources. Cloud computing provides an attractive alternative, simplifying resource provision and enabling reliable replication. We describe our ongoing efforts to cloud-enable a geospatial science gateway hosting general-purpose software building blocks termed GABBs, that provide geospatial data management, analysis, visualization and processing capabilities. We describe the various compute and storage resources and software underlying these building blocks and our automation of the deployment, software installation and configuration of this science gateway on the Amazon Web Services (AWS) cloud platform. Some of the challenges that were encountered and resolved during this cloud-enabling process are also described.
Science gateways have gained wide adoption in recent years as an effective platform for a lower b... more Science gateways have gained wide adoption in recent years as an effective platform for a lower barrier entry to computational resources, research collaboration, dissemination of scientific data, applications and publications, online education, and community engagement. Although multiple portal frameworks and middleware toolkits exist to facilitate the development of a science gateway, the task of bringing data and tools online into a science gateway environment is still daunting for domain science users. In this paper, we describe GABBs, a National Science Foundation funded project that aims to reduce this obstacle by delivering reusable software building blocks for geospatial data management and analysis based on the HUBzero portal platform. The main components of GABBs include a geospatial data management system named iData, libraries for easy creation of geospatial data analysis tools hosted in the gateway, GeoBuilder for creating GIS-enabled data exploration tools without progr...
Science gateways are an integral component of modern collaborative research. They find widespread... more Science gateways are an integral component of modern collaborative research. They find widespread adoption by research groups to share data, code and tools both amongst collaborators on a project and the broader community. However, not unlike research groups, gateways too, face the vagaries of research funding often resulting in a bleak outlook for their maintenance beyond the original project's conclusion. We present a sustainability model based on the HUBzero cyberinfrastructure platform that enables multiple research projects to share a single science gateway allowing for their maintenance even after the original funding source has run out. This model brings with it certain other advantages as well; general improvements to the gateway apply to all hosted projects, similar requirements across projects can often be abstracted into new general purpose capabilities for the gateway which feed back into all hosted projects. Such newly developed capabilities can also foster additional research aiding in new funding proposals that can revitalize and jumpstart hosted dormant projects. We describe a specific instance of a HUBzero science gateway, MyGeoHub, that successfully employs this sustainability model to host several geospatial research
This paper describes the use of cyberinfrastructure to create interactive applications as part of... more This paper describes the use of cyberinfrastructure to create interactive applications as part of the Useful to Usable (U2U) project. These applications transform historical climate data, knowledge, and models into decision support tools for end users such as crop farmers, university Extension educators, and other agricultural advisors. In creating a cyberinfrastructure to support the U2U project, four major challenges have been addressed: designing and developing highly usable web applications with frequent feedback, establishing a software engineering environment to support iterative development, integrating and synthesizing historical and current datasets from a variety of sources (local vs. remote, different access methods, and formats), and supporting project collaboration needs of data and document sharing, project management, and public outreach. The overall goals of the cyberinfrastructure and its architecture design are described. Methods for data retrieval and synthesis, as well as the various software components utilized are discussed. The development and integration of tools into the collaborative HUBzero framework are highlighted, including the use of HUBzero's core features to share ideas, algorithms, and results. A highly iterative development process that includes feedback from experts and end-users to feed requirement definition, design and application updates are also examined.
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
for Applications of Remote Sensing (LARS), was a primary innovator in the field of digital image ... more for Applications of Remote Sensing (LARS), was a primary innovator in the field of digital image analysis and remote sensing of the environment. He and his LARS colleagues, along with a select few other researchers at institutions including the
The author has identified the following significant results. The LACIE field measurement data wer... more The author has identified the following significant results. The LACIE field measurement data were radiometrically calibrated. Calibration enabled valid comparisons of measurements from different dates, sensors, and/or locations. Thermal band canopy results included: (1) Wind velocity had a significant influence on the overhead radiance temperature and the effect was quantized. Biomass and soil temperatures, temperature gradient, and canopy geometry were altered. (2) Temperature gradient was a function of wind velocity. (3) Temperature gradient of the wheat canopy was relatively constant during the day. (4) The laser technique provided good quality geometric characterization.
Photogrammetric Engineering and Remote Sensing, 1986
An experiment is described that examines the effects of solar zenith angle and background reflect... more An experiment is described that examines the effects of solar zenith angle and background reflectance on the composite scene reflectance of small balsam fir (Abies balsamea (L.) Mill.) arranged in different densities. In this study, the shape, density, and, consequently, the needle area index and phytomass of the canopies, as well as the background reflectance, were controlled. The effects of sun angle, view angle, and background reflectance on the multispectral response of small balsam fir trees were significant. Regression models relating spectral vegetation indices (i.e., normalized difference (ND) and greenness (GR) to phytomass) showed very poor relationships for balsam fir canopies with a grass background. However, strong linear relationships were found for ND and GR with phytomass for a background that simulated the reflectance of snow. Changing solar zenith angle significantly affected the models relating ND to phytomass for the snow background, but was not significant in th...
A leaf begins to senesce as soon as it is removed from the plant and changes in metabolic process... more A leaf begins to senesce as soon as it is removed from the plant and changes in metabolic processes and spectral properties are inevitable. If senescence can be delayed for several days without significant changes in spectral properties, then samples of leaves at remote test sites could be prepared and shipped to laboratories which have the equipment to measure spectral properties. The objective of this study was to determine the changes in spectral properties of detached leaves. Leaves from red birch (Betula nigra L.) and red pine (Pinus resinosa Ait.) were immersed for 5 minutes in water or 0.001 M benzylaminopurine (BAP) and stored in plastic bags in the dark at either 5° or 25° C. Total directional-hemispherical reflectance and transmittance of the adaxial surface of birch leaves were measured over the 400 to 1100 nm wavelength region with a spectroradiometer and integrating sphere (LICOR LI-1800). Pine needles were taped together and reflectance of the mat of needles was measured. Spectral properties changed less than 5% of initial values during the first week when leaves were stored at 5° C. Storage at 25° C promoted rapid senescence and large changes in spectral properties. BAP delayed, but did not stop, senescence at 25° C. Low temperature was more effective than BAP in delaying senescence. It appears possible to store leaves at low temperatures in plastic bags in the dark for several days without significantly altering the spectral properties in the 400 to 1100 nm wavelength region.
Percent of total variation in reflectances, greenness and brightness accounted for by soil moistu... more Percent of total variation in reflectances, greenness and brightness accounted for by soil moisture level and significant agronomic factors and interactions.. .. . A-31 Mean agronomic characteristics of spring wheat canopies by soil moisture level and planting date. •. .. .... .. . A-32 Percent correct classification of spring wheat, fallow, and pasture using unitemporal information (Williams Co.
A-3.7. Seasonal changes in four spectral variables and percent soil cover for two row widths in 1... more A-3.7. Seasonal changes in four spectral variables and percent soil cover for two row widths in 1979 for the June 15 planting date. Development stages are indicated for each Page 38 observation date (Russell silt loam). • • • • 39 A-3.8. Seasonal changes in four spectral variables and percent. soil cover for three planting dates in 1979 for 75 cm wide rows. Development stages (Fehr and Caviness, 1977) are indicated for each observation date. Arrows indicate development stages that are unique for that planting date (Russell silt
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