Toby N. Carlson - Profile on Academia.edu (original) (raw)

Papers by Toby N. Carlson

Satellite Remote Sensing of Surface Soil Moisture

Remote Sensing of Energy Fluxes and Soil Moisture Content, 2013

Soil is arguably the Earth’s most valuable nonrenewable resource and undoubtedly the most biologi... more Soil is arguably the Earth’s most valuable nonrenewable resource and undoubtedly the most biologically diverse part of the biosphere. Roughly half of a soil’s volume is composed of mineral and organic content, while the other half consists of pores. Soil moisture (or water) content (SMC) refers to the amount of water in these pores and generally refers to the water contained in the unsaturated soil zone (e.g., Hillel 1998). SMC is affected by the soil texture (determines water holding capacity), topography (affects runoff and infiltration), land cover (influences evapotranspiration), and climate (precipitation, wind, humidity, and solar illumination), and, as a result, SMC is highly variable both in space and time. Although soil moisture comprises only a tiny percentage (~0.001%) of the total global water budget, its importance and influence in the hydrological cycle cannot be understated. It is a key parameter in the exchange of mass and energy at the land surface–atmosphere CONTENTS

The present study investigates the ability of SimSphere, a Soil Vegetation Atmosphere Transfer (S... more The present study investigates the ability of SimSphere, a Soil Vegetation Atmosphere Transfer (SVAT) model, to predict key parameters in characterising land Surface interactions. In particular, the model’s performance in predicting Net Radiation (Rnet), Latent Heat (LE), andSensible Heat (H) was examined. For this purpose, concurrent in-situ measurements of the corresponding parameters for a total of 70 days of the year 2011 from 7 CarboEurope network sites were acquired, incorporating a variety of environmental biomes and climatic conditions in the model evaluation. In overall, SimSphere was largely able to accurately predict the variables against which it was evaluated for most of the experimental sites. Statistical analysis showed highest agreement of H fluxes to the measured in-situ values for all ecosystems, with an average RMSD of 55.36 Wm-2. Predicted LE fluxes and Rnet also agreed well with the corresponding in-situ data with RSMDs of 62.75 Wm-2 and 64.65 Wm-2 respectively....

Geoscientific Model Development, 2013

Sensors, 2009

Soil Vegetation Atmosphere Transfer (SVAT) models consist of deterministic mathematical represent... more Soil Vegetation Atmosphere Transfer (SVAT) models consist of deterministic mathematical representations of the physical processes involved between the land surface and the atmosphere and of their interactions, at time-steps acceptable for the study of land surface processes. The present article provides a comprehensive and systematic review of one such SVAT model suitable for use in mesoscale or boundary layer studies, originally developed by [1]. This model, which has evolved significantly both architecturally and functionally since its foundation, has been widely applied in over thirty interdisciplinary science investigations, and it is currently used as a learning resource for students in a number of educational institutes globally. The present review is also regarded as very timely, since a variation of a method using this specific SVAT model along with satellite observations is currently being considered in a scheme being developed for the operational retrieval of soil surface moisture by the US National Polar-orbiting Operational Environmental Satellite System (NPOESS), in a series of satellites that are due to be launched from 2016 onwards.

Journal of Geophysical Research, 1987

Two-dimensional numerical simulations of the spatial and temporal distributions of Saharan dust s... more Two-dimensional numerical simulations of the spatial and temporal distributions of Saharan dust size distributions over the desert and the eastern Atlantic Ocean are presented. The simulations show that during mobilization the soil size distribution is modified by either a size-dependent lifting mechanism or by mixing of local soil with aged aerosols or with aerosols originating from nearby soils which have different size distributions. The highest number concentrations encountered were not high enough for coagulation to have a significant effect over the time scales considered here. When the source region is near the coast, as opposed to the central Sahara, the highest mass concentration achieved at Sal Island is more than doubled. However, in the two-dimensional simulations the central Saharan storms seem to be equally as important as coastal sources in terms of the optical properties of an outbreak, since the total surface area of the suspended dust at the end of the coastal and inland source simulations are nearly the same. A background mineral aerosol or increased vertical turbulent diffusion across the marine layer inversion is required for the simulated marine layer size distributions to match the observed distributions at particle sizes under 8 •m. Sedimentation prohibits the direct advection of ultragiant particles very far from the coast, suggesting that the ultragiant particles observed over the ocean are locally generated, perhaps in water clouds. 10-9 SAL ISLAND, 780 mb (GATE)-'-SAL ISLAND, 900 mb (GATE) ß SAL ISLAND, SURFACE (JAENICKE AND SCHOTZ, 1978) ß 2000 km WEST OF COAST (SCHOTZ AND JAENICKE, 1976) ß 5000 km WEST OF COAST CAMP DERJ (MEASURED)

Journal of the Atmospheric Sciences, Aug 1, 1988

Earth Observation (EO) provides a promising approach towards deriving accurate spatiotemporal est... more Earth Observation (EO) provides a promising approach towards deriving accurate spatiotemporal estimates of key parameters characterizing land surface interactions, such as latent (LE) and sensible (H) heat fluxes as well as soil moisture content. This paper proposes a very simple method to implement, yet reliable to calculate evapotranspiration fraction (EF) and surface moisture availability (M o) from remotely sensed imagery of Normalized Difference Vegetation Index (NDVI) and surface radiometric temperature (T ir). The method is unique in that it derives all of its information solely from these two images. As such, it does not depend on knowing ancillary surface or atmospheric parameters, nor does it require the use of a land surface model. The procedure for computing spatiotemporal estimates of these important land surface parameters is outlined herein stepwise for practical application by the user. Moreover, as the newly developed scheme is not tied to any particular sensor, it can also be implemented with technologically advanced EO sensors launched recently or planned to be launched such as Landsat 8 and Sentinel 3. The latter offers a number of key advantages in terms of future implementation of the method and wider use for research and practical applications alike.

The numerical simulation of the evolution of a Saharan dust outbreak by using a general prognostic aerosol model

A three-dimensional model is developed that explicitly predicts the evolution of the spatial dist... more A three-dimensional model is developed that explicitly predicts the evolution of the spatial distributions of aerosols utilizing a time-dependent, initial value prognostic aerosol model based on aerosol physicochemical processes, a knowledge of aerosol sinks and sources, and the predicted motions of the atmosphere. These models serve a useful purpose in determining standardized aerosol spectra for utilization in radiative transfer calculations. The first numerical prediction of a Saharan dust outbreak evolution is described. It is shown that the results are in qualitative agreement with measurements despite the fact that in this preliminary simulation the generation of the dust depended upon several empirically based assumptions. IR satellite photographs taken during GATE are being examined in an attempt to determine the sources of the dust.

Modelling key parameters characterising land surface using the SimSphere SVAT model

Agricultural Water Management, 2021

Abstract The present study investigates the ability of SimSphere, a soil vegetation atmosphere tr... more Abstract The present study investigates the ability of SimSphere, a soil vegetation atmosphere transfer model, to predict key parameters in characterising land surface interactions. In particular, the model's performance in predicting Net Radiation (Rnet), Latent Heat (LE) and Sensible Heat (H) was examined. For this purpose, concurrent in-situ measurements of the corresponding parameters for a total of 70 days of the year 2011 from seven CarboEurope network sites were acquired, incorporating a variety of environmental biomes and climatic conditions in the model evaluation. In overall, SimSphere was largely able to accurately predict the variables against which it was evaluated for most of the experimental sites. Statistical analysis showed highest agreement of H fluxes to the measured in-situ values for all ecosystems, with an average root mean square difference of 55.36 Wm−2. Predicted latent fluxes and Rnet also agreed well with the corresponding in-situ data with RSMDs of 62.75 and 64.65 Wm−2, respectively. Our findings contribute towards a better understanding of the model structure, functioning and its correspondence to the real-world system. They also further establish its capability as a useful teaching and research tool in modelling Earth's land surface interactions. This is important given its increasing use, including its synergies with Earth observation data.

Remote Sensing, 2020

Earth Observation (EO) makes it possible to obtain information on key parameters characterizing i... more Earth Observation (EO) makes it possible to obtain information on key parameters characterizing interactions among Earth’s system components, such as evaporative fraction (EF) and surface soil moisture (SSM). Notably, techniques utilizing EO data of land surface temperature (Ts) and vegetation index (VI) have shown promise in this regard. The present study investigates, for the first time, the accuracy of one such technique, known as the “simplified triangle”, using Sentinel-3 EO data, acquired for 44 days in 2018 at three savannah FLUXNET sites in Spain. The technique was found to be able to predict both EF and SSM with reasonable accuracy when compared to collocated ground measurements. Comparisons performed for all days together showed relatively low Root Mean square Difference (RMSD) for both EF (0.191) and SSM (0.012 cm3 cm−3) and good correlation coefficients (R) of 0.721 and 0.577, respectively. Both EF and SSM were also largely in agreement with land cover and seasonal varia...

Coupling remote sensing with a water balance model for soybean yield predictions over large areas

Earth Science Informatics, 2019

In this study a new method for predicting soybean yield over large spatial scales, overcoming the... more In this study a new method for predicting soybean yield over large spatial scales, overcoming the difficulties of scalability, is proposed. The method is based on the so-called “simplified triangle” remote sensing technique which is coupled with a crop prediction model of Doorenbos and Kassam 1979 (DK) and the climatological water balance model of Thornthwaite and Mather 1955 (ThM). In the method, surface soil water content (Mo), evapotranspiration (ET), and evaporative fraction (EF) are derived from satellite-derived surface radiant temperature (Ts) and normalized difference vegetation index (NDVI). Use of the proposed method is demonstrated in Brazil’s Paraná state for crop years 2002–03 to 2011–12. The soybean crop yield model of DK is evaluated using remotely estimated EF values obtained by a simplified triangle. Predicted crop yield by the satellite measurements and from archived Tropical Rainfall Measuring Mission data (TRMM) and European Centre for Medium-Range Weather Forecasts (ECMWF) data were in good agreement with the measured crop yield. A “d 2 ” index (modified Willmott) between 0.8 and 0.98 and RMSE between 30.8 (kg/ha) to 57.2 (kg/ha) was reported. Crop yield predicted using EF from the triangle were statistically better than the DK and ThM using values of the equivalent of EF obtained from archived surface data when compared with the measured soybean crop data. The proposed method requires no ancillary meteorological or surface data apart from the two satellite images. This makes the technique easy to apply allowing providing spatiotemporal estimates of crop yield in large areas and at different spatial scales requiring little or no surface data.

Estimation of Energy Fluxes and Soil Moisture Content from AATSR, MERIS and SimSphere Model

Sensitivity analysis (SA) consists of an integral and important validatory check of a computer si... more Sensitivity analysis (SA) consists of an integral and important validatory check of a computer simulation model before it is used to perform any kind of analysis. In the present work, we present the results from a SA performed on the SimSphere Soil Vegetation Atmosphere Transfer (SVAT) model utilising a cutting edge and robust Global Sensitivity Analysis (GSA) approach, based on the use of the Gaussian Emulation Machine for Sensitivity Analysis (GEM-SA) tool. The sensitivity of the following model outputs was evaluated: the ambient CO2 concentration and the rate of CO2 uptake by the plant, the ambient O3 concentration, the flux of O3 from the air to the plant/soil boundary, and the flux of O3 taken up by the plant alone. The most sensitive model inputs for the majority of model outputs were related to the structural properties of vegetation, namely, the Leaf Area Index, Fractional Vegetation Cover, Cuticle Resistance and Vegetation Height. External CO2 in the leaf and the O3 concent...

The object of this research is to use indirect measurements, notably thermal infrared, to describ... more The object of this research is to use indirect measurements, notably thermal infrared, to describe urbanization and deforestation with parameters that can be used to assess, as well as predict, the effects of land use changes on local microclimate. More specifically, we use a new approach for the treatment of remotely sensed data; this is referred to as the 'triangle' method. The name triangle is given because the envelope of data points, when plotted as a function of surface radiant temperature versus vegetation index or fractional vegetation cover, exhibits the shape of a triangle. From the information contained on these 'scatter plots', land use changes can be related to two intrinsic surface variables, the surface moisture availability (M(sub 0))(sup 1) and fractional vegetation cover. Recent work by Carlson et al. indicate that the triangle shape on the scatter plots may be scale similar, suggesting that these two parameters are subject to the same interpretatio...

Remotely-sensed Surface Parameters Governing Urban Climate Change

Environmental Modelling & Software, 2015

Retrieval of surface energy fluxes and of soil surface moisture content via the combination of a SVAT model and ASTER imagery analysis

ABSTRACT Estimation of land-atmosphere fluxes and related land surface parameters is of key impor... more ABSTRACT Estimation of land-atmosphere fluxes and related land surface parameters is of key importance in many disciplines including hydrology, meteorology and agriculture. Remote sensing alone or often combined with land surface simulation process models, such as Soil Vegetation Atmosphere Transfer (SVAT) models, has generally shown a promising avenue in the estimation of these parameters from space. The present study investigates in a European setting the use of one such scheme which is based on the combined use of SimSphere one-dimensional SVAT model with multispectral satellite data from the Advanced Spaceborne Thermal Emission and Reflection Scanning Radiometer (ASTER). The ability of the studied method to resolve for the land surface energy fluxes and of soil surface moisture content is verified using validated ground observations obtained from selected days collected from nine CARBOEUROPE sites representing a variety of climatic, topographic and environmental conditions. Results indicated a close agreement between the compared parameters both spatially and temporally with accuracies comparable to those obtained in similar experiments with high spatial resolution data. Overall performance of the examined here methodology was also found to be affected by the model initialisation conditions representative of the test site environment, predominantly the atmospheric conditions required in the SVAT model initial conditions. This study represents the first comprehensive evaluation of the performance of this particular methodological implementation at a European setting using the SimSphere model with the ASTER data. In addition, it is very timely, given that a variation of the examined here methodology has been proposed for the operational retrieval of the soil surface moisture content by National Polar-orbiting Operational Environmental Satellite System (NPOESS), in a series of satellite platforms due to be launched from 2016.

Deriving Surface Soil Moisture from Medium Resolution VNIR/TIR Earth Observation Data combined with 1D simulation process model

Deriving regional estimates of energy fluxes from space from the synergy of AATSR Imagery with a land surface process model