Measurements Of Soil Heat Flux Research Articles

A distributed-temperature-sensing-based soil temperature profiler

Abstract. Storage change in heat in the soil is one of the main components of the energy balance and is essential in studying the land–atmosphere heat exchange. However, its measurement proves to be difficult due to (vertical) soil heterogeneity and sensors easily disturbing the soil. Improvements in the precision and resolution of distributed temperature sensing (DTS) equipment has resulted in its widespread use in geoscientific studies. Multiple studies have shown the added value of spatially distributed measurements of soil temperature and soil heat flux. However, due to the spatial resolution of DTS measurements (∼30 cm), soil temperature measurements with DTS have generally been restricted to (horizontal) spatially distributed measurements. This paper presents a device which allows high-resolution measurements of (vertical) soil temperature profiles by making use of a 3D-printed screw-like structure. A 50 cm tall probe is created from segments manufactured with fused-filament 3D printing and has a helical groove to guide and protect a fiber-optic (FO) cable. This configuration increases the effective DTS measurement resolution and will inhibit preferential flow along the probe. The probe was tested in the field, where the results were in agreement with the reference sensors. The high vertical resolution of the DTS-measured soil temperature allowed determination of the thermal diffusivity of the soil at a resolution of 2.5 cm, many times better than what is feasible using discrete probes. A future improvement in the design could be the use of integrated reference temperature probes, which would remove the need for DTS calibration baths. This could, in turn, support making the probes “plug and play” into the shelf instruments without the need to splice cables or experience in DTS setup design. The design can also support the integration of an electrical conductor into the probe and allow heat tracer experiments to derive both the heat capacity and the thermal conductivity over depth at high resolution.

Thermal conductivity in a vadose zone: A novel spectral solution and application by the implication of significant coherence of thermal condition in the shallow soil water layer

AbstractIn the context of the heterogeneity in the unsaturated or vadose zone, accurately representing the analytical mechanisms and in‐situ water content within the soil layer poses a significant challenge. Particularly in shallow layers, thermal conditions exhibit rapid changes in response to evolving surface temperatures. This study proposes a hypothesis suggesting that the in situ heat mechanism may notably impact the soil water layer. The research introduces an innovative approach to theoretically uncover thermal conditions, including soil temperature, soil temperature gradients, and heat flux, within the shallow Quaternary gravel layer at various depths through spectral analysis of temporal observations. The study presents a stochastic inverse solution to estimate thermal conductivity by leveraging spectral analysis of soil heat flux and temperature gradients. The findings reveal that thermal conditions exhibit the most prominent periodic fluctuations during the diurnal process over a 24‐hour cycle. The soil temperature gradients and heat flux measurements at depths of 0.1, 0.3, 0.6, and 1.2 m demonstrate their ability to capture changes in soil temperature and air temperature to a certain extent within the frequency domain. Furthermore, the analysis highlights the intrinsic uncertainty and sensitivity of estimating thermal conductivity in heterogeneous soil environments. The wide variability observed in thermal conductivity values, coupled with their dependence on soil type and environmental conditions, underscores the need for careful consideration of these factors in future studies and modeling efforts. Applying the derived inverse spectral solution allows for determining thermal conductivity throughout the soil‐water system across depths ranging from 0.1 to 1.2 m. As a result, this research demonstrates the feasibility and practicality of assessing the thermal conductivity of the soil layer in conjunction with heat flux and temperature gradients through spectral analysis.

Experiments and COMSOL simulations: A comparative study of the heat flux plate method and the gradient method for soil heat flux measurements in barren sand

Soil heat flux (G) is important for studying the energy balance at the soil-atmosphere interface. In most cases, a reference flux (true value) is not available for soil heat flux. The heat flux plate method and the heat pulse sensor gradient method are two commonly used methods to measure soil heat flux. Both methods have inherent shortcomings that lead to unavoidable measurement errors. There is a need for a theoretical analysis to identify the origin of errors associated with the gradient method. In this study, by introducing a plane heater of known heating strength to generate a one-dimensional heat flux, we compared the measurements of soil heat flux by both methods at different soil moisture contents for laboratory (indoor) and field (outdoor) experiments, as well as computer simulations for a sandy soil. Differences between the COMSOL simulation results and the indoor measurements were less than 15%, indicating that the COMSOL simulated soil heat flux results were reliable. The indoor experiments provided close agreement between the heat flux plate method and the gradient method (Pearson's correlation coefficient r ≥ 0.993). The results of the field experiments showed that the correlation coefficient of the two methods decreased by at least 9.3%. Our field measurements indicated that the gradient method is not suitable for measuring G in the presence of alternating freezing-thawing soil conditions. Although heat flux plates have several short-comings, they may perform better than the heat pulse sensor gradient method in partially frozen soils. The finite difference approximation of nonlinear thermal gradients causes errors in the gradient method heat flux values. However, this gradient method error could be eliminated by altering the heat pulse probe positioning with depth to provide finer scale measurements of temperature with depth.

Influence of Different Methods to Estimate the Soil Thermal Properties from Experimental Dataset

Knowledge of soil thermal properties (diffusivity (k) and conductivity (λ)) is important to understand the soil–plant–atmosphere interaction related to the physical and biological processes associated with energy transfer and greenhouse gas exchanges. The incorporation of all the physical processes that occur in the energy transfer in the soil is a challenge in order to correctly estimate soil thermal properties. In this work, experimental measurements of soil temperature and soil heat flux obtained in a silty clay loam soil covered by native grassland located in the Brazilian Pampa biome were used to estimate soil thermal properties using different methods including the influence of the soil water content at different soil depths in heat transfer processes. The λ was estimated using the numerical solution of the Fourier equation by the Gradient and Modified Gradient methods. For the surface layer, the results for both models show large variability in daily values, but with similar values for the annual mean. For λ at different soil depths, both models showed an increase of approximately 50% in the λ value in the deeper layers compared to the surface layer, increasing with depth in this soil type. The k was estimated using analytical and numerical methods. The analytical methods showed a higher variability and overestimated the values of the numerical models from 15% to 35%. The numerical models included a term related to the soil water content. However, the results showed a decrease in the mean value of k by only 2%. The relationship between thermal properties and soil water content was verified using different empirical models. The best results for thermal conductivity were obtained using water content in the surface layer (R2 > 0.5). The cubic model presented the best results for estimating the thermal diffusivity (R2 = 0.70). The analyses carried out provide knowledge for when estimating soil thermal properties using different methods and an experimental dataset of soil temperature, heat flux and water content, at different soil depths, for a representative soil type of the Brazilian Pampa biome.

Estimating Bulk Stomatal Conductance in Grapevine Canopies

In response to changes in their environments, grapevines regulate transpiration using various physiological mechanisms that alter conductance of water through the soil-plant-atmosphere continuum. Expressed as bulk stomatal conductance at the canopy scale, it varies diurnally in response to changes in vapor pressure deficit and net radiation, and over the season to changes in soil water deficits and hydraulic conductivity of both the soil and plant. To help with future characterization of this dynamic response, a simplified method is presented for determining bulk stomatal conductance based on the crop canopy energy flux model by Shuttleworth and Wallace using measurements of individual vine sap flow, temperature and humidity within the vine canopy, and estimates of net radiation absorbed by the vine canopy. The methodology presented respects the energy flux dynamics of vineyards with open canopies, while avoiding problematic measurements of soil heat flux and boundary layer conductance needed by other methods, which might otherwise interfere with ongoing vineyard management practices. Based on this method and measurements taken on several vines in a non-irrigated vineyard in Bordeaux France, bulk stomatal conductance was estimated on 15-minute intervals from July to mid-September 2020 producing values similar to those presented for vineyards in the literature. Time-series plots of this conductance show significant diurnal variation and seasonal decreases in conductance associated with increased vine water stress as measured by predawn leaf water potential. Global sensitivity analysis using non-parametric regression found transpiration flux and vapor pressure deficit to be the most important input variables to the calculation of bulk stomatal conductance, with absorbed net radiation and bulk boundary layer conductance being much less important. Conversely, bulk stomatal conductance was one of the most important inputs when calculating vine transpiration, emphasizing the usefulness of characterizing its dynamic response for the purpose of estimating vine canopy transpiration in water use models.

Experiments and Comsol Simulations: A Comparative Study of the Heat Flux Plate Method and the Gradient Method for Soil Heat Flux Measurements

Experiments and Comsol Simulations: A Comparative Study of the Heat Flux Plate Method and the Gradient Method for Soil Heat Flux Measurements

Evaluating surface renewal models for estimating sensible heat flux above and within a coffee agroforestry system

The surface renewal method offers an inexpensive way to estimate the sensible heat flux (H). When combined with measurements of net radiation and soil heat flux, latent heat flux (evapotranspiration) can be estimated indirectly. This study evaluated the performance of two surface renewal models to estimate H in a traditional coffee agroforestry system. The first model (Snyder96) is the commonly used approach in which H is calculated from the average temperature ramp amplitude and duration, which in turn are calculated from the 2nd, 3rd, and 5th order structure functions. The second model (Chen97) is a reformulation of Snyder96 in which H is calculated from the 3rd order structure function and friction velocity (u*). The models were calibrated and evaluated with eddy covariance data. Tests were conducted at three levels (above-canopy, above-coffee, above-ground), with each level having two replicate plots. Both models showed generally good agreement with the observations when using humidity-corrected sonic temperature data. Estimates from Chen97 agreed slightly better with measurements than those from Snyder96. In addition, the results suggest that for Chen97 the same calibration can be used for the above-canopy and above-coffee levels and for positive and negative H. Also for the above-ground level the combined empirical coefficient of Chen97 was similar to those for the other levels, but the variability between plots was too high to draw conclusions. Conversely, the results showed that Snyder96 requires separate calibrations for each level and for positive and negative H. For Chen97, similarly good results were obtained when using frequency response-corrected thermocouple data. For Snyder96, results were also good above the canopy, but not within the canopy, particularly close to the ground. Chen97 needs wind speed to calculate u*. Wind speed is needed for both models if the signals of thicker, stronger thermocouples are corrected for the frequency response error.

Estimation of Sensible and Latent Heat Fluxes Using Surface Renewal Method: Case Study of a Tea Plantation

An experiment of sensible and latent heat flux measurement was conducted in a tea plantation near the Yangtze River within Danyang of Jiangsu Province, China. High-frequency (~10 Hz) air temperature measurement with fine-wire thermocouples (⌀ = 50 μm) was used for the estimation of sensible heat flux (H), and latent heat flux (LE) was extracted as a residual of the energy balance equation using additional measurements of net radiation (Rn) and soil heat flux (G). Results were compared against the eddy covariance (EC) system under unstable conditions only, and days with high precipitation were excluded from further analysis. Half-hourly datasets of the sensible heat flux estimated using the surface renewal method (SR) (HSR) and measured by the EC system (HEC) were analyzed. Results showed good agreement with R2 = 0.80, root mean square error (RMSE) = 27.87 W m−2, relative error (RE) = 9.02%, and a regression slope of 0.68—this slope was used for the calibration of the uncalibrated HSR estimated by SR. On the other hand, the half-hourly dataset of LESR was regressed against EC, and it showed good agreement with relatively high R2 = 0.93, RMSE = 32.99 W·m−2, and RE = 5.67%. Hence, the SR method may estimate the surface fluxes at a relatively low cost, ultimately improving calculations of evapotranspiration. Thus, the SR method could provide an economical tool for improving crop water management of tea plantations.

Imaging the Salinelle Mud Volcanoes (Sicily, Italy) using integrated geophysical and geochemical surveys

Geochemical and geophysical prospecting methods (including measurements of soil heat flux and soil CO2 flux, gravimetry, self-potential and geomagnetism) are used to produce an integrated data set aimed at imaging the migration of fluids in the sub-surface at the Salinelle mud volcanoes, located on the lower southwestern flank of Mt Etna (Sicily, Italy). This area was affected by magmatic eruptions from local volcanic centers between about 48 and 27 ka. Today, only pseudo-volcanic phenomena due to over-pressured multiphase pore fluids there occur. Carbon dioxide of magmatic origin, mixed with biogenic hydrocarbons, warm hypersaline waters and mud, are constantly released at the surface through the main conduits of mud volcanoes, whose activity is characterized by alternation of mild gas bubbling periods and strong paroxysmal phases. The latter produce violent gas eruptions that eject warm water (T ≈ 50° C) to a height up to about 1 m. Surface distribution of the geophysical and geochemical parameters have been investigated to detect the main pathways through which fluids move toward the shallow crust. Integration of geochemical, geophysical and geological maps allowed for the tracing of the fluid flow in the shallowest (a few tens of meters below the surface) part of the local hydrothermal system. Our results showed that the rising of fluids from a deep reservoir is controlled by the main structural and geological features of the area and their temporal and spatial evolution depends on pressure conditions inside the hydrothermal system.

A Numerical Model to Estimate the Soil Thermal Conductivity Using Field Experimental Data

Soil thermal conductivity is an important parameter for understanding soil heat transfer. It is difficult to measure in situ with available instruments. This work aims to propose a numerical model to estimate the thermal conductivity from the experimental measurements of soil heat flux and soil temperature. The new numerical model is based on the Fourier Law adding a constant empirical parameter to minimize the uncertainties contained in the data from field experiments. Numerically, the soil thermal conductivity is obtained by experimental linear data fitting by the Least Squares Method (LSM). This method avoids numerical indetermination when the soil temperature gradient or soil heat flux is very close to zero. The new model is tested against the different numerical methodology to estimate the soil heat flux and validated with field experimental data. The results indicate that the proposed model represents the experimental data satisfactorily. In addition, we show the influence of the different methodologies on evaluating the dependence of the thermal conductivity on the soil water content.

Simple and Reliable methods of Estimating Ground Heat Flux at a Tropical location in Nigeria

Ground heat flux (Go) plays an important role in the partitioning of energy budget at earth’s surface. The estimates of G0 are required as part of boundary conditions by all general circulation models. In this work, reliability of four simple and computationally cheap models was tested against a more complex and reliable model as the reference. The simple models selected for investigation are: Simple measurement (SM), Percentage of net radiation (PR), Universal function of net radiation (UR), and Linear function of net radiation (LR) models. Force restore model (FR) was used as the reference model.The data of soil temperature measured at the surface and 0.05 m depth, soil heat flux, measured at 0.05m, and net radiation were obtained from Nigerian Micrometeorological Experiment, Ile Ife. Force restore model was first calibrated with direct measurements for soil heat flux at 0.05 m depth with satisfactory result before it was employed to generate reference G0 estimates. Estimates of SM, PR, UR and LR were compared with FR using simple statistics of coefficient of determination (R2), slope, intercept, root mean square error (RMSE) and mean bias error (MBE).The SM model reproduced the day-time and night-time variations of G0 better than all the models that parameterized G0 as a function of net radiation (R2slope, intercept, RMSE and MBE values of 0.85, 0.87, 3.43W/m232.69, W/m2-3.70 W/m2 respectively). This model however requires measurement of both soil heat flux and temperature. The LR model generated the best estimates of Go out of all the models that utilized net radiation measurements (R2slope, intercept, RMSE and MBE values are 0.60, 0.58,4.55 W/m2, 53.81 W/m23.60 W/m2 respectively) while UR model is the worst. The LR model, though depend only on one measurement, requires site-specific calibrations and can therefore be deployed for gap filling where SM model cannot be used

Fetch Effect on Flux-Variance Estimations of Sensible and Latent Heat Fluxes of Camellia Sinensis

Precise estimation of surface-atmosphere exchange is a major challenge in micrometeorology. Previous literature presented the eddy covariance (EC) as the most reliable method for the measurements of such fluxes. Nevertheless, the EC technique is quite expensive and complex, hence other simpler methods are sought. One of these methods is Flux-Variance (FV). The FV method estimates sensible heat flux (H) using high frequency (~10Hz) air temperature measurements by a fine wire thermocouple. Additional measurements of net radiation (Rn) and soil heat flux (G) allow the derivation of latent heat flux (LE) as the residual of the energy balance equation. In this study, the Flux Variance method was investigated, and the results were compared against eddy covariance measurements. The specific goal of the present study was to assess the performance of the FV method for the estimation of surface fluxes along a variable fetch. Experiment was carried out in a tea garden; an EC system measured latent and sensible heat fluxes and five fine-wire thermocouples were installed towards the wind dominant direction at different distances (fetch) of TC1 = 170 m, TC2 = 165 m, TC3 = 160 m, TC4 = 155 m and TC5 = 150 m from the field edge. Footprint analysis was employed to examine the effect of temperature measurement position on the ratio between 90% footprint and measurement height. Results showed a good agreement between FV and EC measurements of sensible heat flux, with all regression coefficients (R2) larger than 0.6; the sensor at 170 m (TC1), nearest to the EC system, had highest R2 = 0.86 and lowest root mean square error (RMSE = 25 Wm−2). The estimation of LE at TC1 was also in best agreement with eddy covariance, with the highest R2 = 0.90. The FV similarity constant varied along the fetch within the range 2.2–2.4.

Development of a Low-Cost Soil Heat Flux and Temperature Profile with Logger

Variation of soil temperature and soil heat flux measurements from a locally fabricated and calibrated device were analyzed and compared with a standard device. The soil heat flux consists of two-disc aluminum plates, dielectric material and two thermocouples such that each thermocouple was sandwiched between the aluminum plates and one side of the dielectric material. The sizes of the aluminum plates and the dielectric material were 32 mm in diameter and their thickness is 2.5 mm. Differential temperature between two thermocouples attached to two aluminum plates separated by a thermal insulator was used to measure the soil heat flux values. The thermocouples amplifier module AD8495 and then combined with a 16-bit Analog to Digital Converter (ADS1115) for a good measurement resolution was employed for the signal conditioning. A semiconductor sensor DS18B20 was used to measure the soil temperature. The microSD shield was included for storing data and DS3232, a Real Time Clock (RTC) module for timekeeping. Arduino mega 2560 microcontroller was used to coordinate the whole active and display the activities on LCD. The soil heat flux sensor was calibrated using the principle of thermal conduction over the surface area by heating with a known heat source. The thermal conductivity of heat flux is given by 3.3407 (WV-1m-1) from the empirical deduction. The temperature sensing unit was checked for accuracy by inserting it inside a calorimeter with the mercury-in-glass thermometer and the correlation obtained was 0.92. The soil heat flux and temperature sensing unit were compared with that of standard Campbell device. The correlation obtained for soil heat flux and temperature were 0.89 and 0.95 respectively. The result obtained when installed at the Redeemer’s University, Ede, Nigeria, the variation of soil heat flux and temperature when placed at the same level of 10 cm into the soil gave the same value. The maximum peak of heat flux density usually occurs at about 13:00 pm to 15:00 pm with values around 260 W/m2 at 10 cm. The logging interval can be preset to any rate from 30 seconds and above.

Surface Renewal Application for Estimating Evapotranspiration: A Review

The estimation of evapotranspiration (ET) is essential for meteorological modeling of surface exchange processes, as well as for the agricultural practice of irrigation management. Hitherto, a number of methods for estimation of ET at different temporal scales and climatic conditions are constantly under investigation and improvement. One of these methods is surface renewal (SR). Therefore, the premise of this review is to present recent developments and applications of SR for ET measurements. The SR method is based on estimating the turbulent exchange of sensible heat flux between plant canopy and atmosphere caused by the instantaneous replacement of air parcels in contact with the surface. Additional measurements of net radiation and soil heat flux facilitate extracting ET using the shortened energy balance equation. The challenge, however, is the calibration of SR results against direct sensible heat flux measurements. For the classical SR method, only air temperature measured at high frequency is required. In addition, a new model suggests that the SR method could be exempted from calibration by measuring additional micrometeorological variables. However, further improvement of the SR method is required to provide improved results in the future.

A novel approach to evaluate soil heat flux calculation: An analytical review of nine methods

AbstractThere are no direct methods to evaluate calculated soil heat flux (SHF) at the surface (G0). Instead, validation and cross evaluation of methods for calculating G0 usually rely on the conventional calorimetric method or the degree of the surface energy balance closure. However, there is uncertainty in the calorimetric method itself, and factors apart from G0 also contribute to nonclosure of the surface energy balance. Here we used a novel approach to evaluate nine different methods for calculating SHF, including the calorimetric method and methods based on analytical solutions of the heat diffusion equation. The SHF (Gz) measured by a self‐calibrating SHF plate at a depth of z = 5 cm below the surface (hereafter Gm_5cm) was deployed as a reference. Each SHF calculation method was assessed by comparing the calculated Gz at the same depth (hereafter Gc_5cm) with Gm_5cm. The calorimetric method and simple measurement method performed best in determining Gc_5cm but still underestimated Gm_5cm by 19% during the daytime. Possible causes for this underestimation include errors and uncertainties in SHF measurements and soil thermal properties, as well as the phase lag between Gc_5cm and Gm_5cm. Our results indicate that the calorimetric method achieves the most accurate SHF estimates if self‐calibrating SHF plates are deployed at two depths (e.g., 5 cm and 10 cm), soil temperature and water content measurements are made in a few depths between the two plates, and soil thermal properties are accurately quantified.

Bark beetle-induced tree mortality alters stand energy budgets due to water budget changes

Insect outbreaks are major disturbances that affect a land area similar to that of forest fires across North America. The recent mountain pine bark beetle (Dendroctonus ponderosae) outbreak and its associated blue stain fungi (Grosmannia clavigera) are impacting water partitioning processes of forests in the Rocky Mountain region as the spatially heterogeneous disturbance spreads across the landscape. Water cycling may dramatically change due to increasing spatial heterogeneity from uneven mortality. Water and energy storage within trees and soils may also decrease, due to hydraulic failure and mortality caused by blue stain fungi followed by shifts in the water budget. This forest disturbance was unique in comparison to fire or timber harvesting because water fluxes were altered before significant structural change occurred to the canopy. We investigated the impacts of bark beetles on lodgepole pine (Pinus contorta) stand and ecosystem level hydrologic processes and the resulting vertical and horizontal spatial variability in energy storage. Bark beetle-impacted stands had on average 57 % higher soil moisture, 1.5 °C higher soil temperature, and 0.8 °C higher tree bole temperature over four growing seasons compared to unimpacted stands. Seasonal latent heat flux was highly correlated with soil moisture. Thus, high mortality levels led to an increase in ecosystem level Bowen ratio as sensible heat fluxes increased yearly and latent heat fluxes varied with soil moisture levels. Decline in canopy biomass (leaf, stem, and branch) was not seen, but ground-to-atmosphere longwave radiation flux increased, as the ground surface was a larger component of the longwave radiation. Variability in soil, latent, and sensible heat flux and radiation measurements increased during the disturbance. Accounting for stand level variability in water and energy fluxes will provide a method to quantify potential drivers of ecosystem processes and services as well as lead to greater confidence in measurements for all dynamic disturbances.

Soil heat flux and air temperature as factors of radon (Rn-222) concentration in the near-ground air layer

AbstractA unique, highly time-resolved, and synchronous three-year dataset of near-surface atmospheric radon-222 as well as soil heat flux and air temperature measurements at two sites (rural and urban) in Central Poland are investigated. The recognition of temporal variability of Rn-222 and selected meteorological variables in the urban and rural areas served to create two statistical models for estimation of this radionuclide concentration at 2 m a.g.l. The description of the relationships between the variables for individual months was established on the basis of an exponential function and an exponential function with time derivative of predictor to account for the hysteresis issue. The model with time derivative provided better results. The weakest fitting of modelled data to empirical ones is observed for the winter months. During subsequent seasons, air temperature as well as QG-driven (soil heat flux) models exhibited very high agreement with the empirical data (MBE, RMSE, MAE, and ‘index of agreement’ by Willmott were used to evaluate the models). A restriction in the use of QG for Rn-222 concentration was observed only in winter in the case of snow cover occurrence, which reduces the daily QG variability.

Experimental investigation of subsurface soil water evaporation on soil heat flux plate measurement

Accurate measurement of soil heat flux is required to describe the heat and mass transfer in soil. In this study, results of soil heat flux derived through the single probe and three needle gradient methods were compared with those obtained via the plate method. Field test was conducted on a bare loamy sand at 1-cm depth and a bare loam at 10-cm depth. Results from the two gradient methods revealed good agreement on flux measurement. The evaporation rate was relatively large on loamy sand, and the flux magnitude measured by the two gradient methods was 1.5 times higher than that of the plate method at 1-cm depth. However, the flux underestimation of the plate method was not observed at 10-cm depth of the bare loam in which the evaporation rate was negligible. Thus, the blockage of vapor transfer from the impervious plates primarily explained the heat flow divergence between the plate and gradient methods. Needle-type sensors exhibited a slight disturbance on the soil over the plate method, which may improve measurement accuracy. Heat flux plates must be placed relatively deep in the soil profile (e.g., 10 cm) to minimize measurement errors.

Spatial and temporal variability in spectral-based surface energy evapotranspiration measured from Landsat 5TM across two mangrove ecotones

Coastal mangroves lose large amounts of water through evapotranspiration (ET) that can be equivalent to the amount of annual rainfall in certain years. Satellite remote sensing can play a crucial role in identifying regional ET trends and surface energy changes after disturbances in isolated and inaccessible areas of coastal mangrove wetlands, like those found in Everglades National Park in southern Florida. Using a combination of long-term datasets acquired from the NASA Landsat 5TM satellite database and the Florida Coastal Everglades Long-Term Ecological Research project, the present study investigates how ET as well as radiation and other energy balance parameters in the Everglades mangrove ecotone have responded to multiple hurricane events and restoration projects over the past two decades. An energy balance model using satellite data was used to estimate latent heat (λE) in tall and scrub mangrove environments. An eddy-covariance tower and weather tower supplied long-term data of multiple environmental and meteorological parameters that were used in calibrating and testing the modeled results from the Landsat images. Results identified significant differences in λE and soil heat flux measurements between the tall and scrub, and fringe and basin mangrove environments. The scrub mangrove site had the lowest λE rates, highest soil heat flux and lowest biophysical index (i.e., Fractional Vegetation Cover (FVC), Normalized Difference Vegetation Index (NDVI), and Soil-Adjusted Vegetation Index (SAVI) values. Mangrove damage and mortality associated with two strong hurricanes decreased FVC, NDVI, and SAVI, and increased soil heat flux at the tall mangrove site located in a basin-type environment. Recovery of the spectral characteristics, energy balance parameters and λE following hurricane disturbance was quicker in fringe mangroves than in basin mangroves. Latent heat fluxes (λE) were also relatively high after each storm and may have increased as a result of increasing vapor pressure deficits. Remote sensing of the surface energy balance and λE of mangrove forests can help our understanding of how these environments respond to disturbances to the landscape and the effect that these changes can have on the energy and water budget. Moreover, relationships between energy and water balance components developed for the coastal mangroves of southern Florida could be extrapolated to other mangrove systems in the Caribbean to measure changes caused by natural events and human modifications.

A new method to measure Bowen ratios using high-resolution vertical dry and wet bulb temperature profiles

Abstract. The Bowen ratio surface energy balance method is a relatively simple method to determine the latent heat flux and the actual land surface evaporation. The Bowen ratio method is based on the measurement of air temperature and vapour pressure gradients. If these measurements are performed at only two heights, correctness of data becomes critical. In this paper we present the concept of a new measurement method to estimate the Bowen ratio based on vertical dry and wet bulb temperature profiles with high spatial resolution. A short field experiment with distributed temperature sensing (DTS) in a fibre optic cable with 13 measurement points in the vertical was undertaken. A dry and a wetted section of a fibre optic cable were suspended on a 6 m high tower installed over a sugar beet trial plot near Pietermaritzburg (South Africa). Using the DTS cable as a psychrometer, a near continuous observation of vapour pressure and air temperature at 0.20 m intervals was established. These data allowed the computation of the Bowen ratio with a high spatial and temporal precision. The daytime latent and sensible heat fluxes were estimated by combining the Bowen ratio values from the DTS-based system with independent measurements of net radiation and soil heat flux. The sensible heat flux, which is the relevant term to evaluate, derived from the DTS-based Bowen ratio (BR-DTS) was compared with that derived from co-located eddy covariance (R2 = 0.91), surface layer scintillometer (R2 = 0.81) and surface renewal (R2 = 0.86) systems. By using multiple measurement points instead of two, more confidence in the derived Bowen ratio values is obtained.