Rapid Estimation of Coniferous Forest Leaf Area Index Using a Portable Integrating Radiometer

Canopy transmittance was measured at 1200 and 1400 local solar time using an integrating radiometer on seven coniferous forest stands in western Montana, ranging in projected leaf area index (LAI) from 1.7—5.3 m2/m2. Transmittance of each 1—ha stand was measured at 96,000 points, yet measurement required \u3c1 h because the instrument instantaneously integrates 80 radiometer measurements at once. The Beer—Lambert Law was inverted to estimate LAI using measured transmittance and an extinction coefficient of 0.52. LAI estimated by transmittance was highly correlated with LAI measured by sapwood—based allometric equations at both the 1200 (R2 = 0.97) and 1400 (R2 = 0.94) measurement times. The results suggest that the technique has a wide applicability given the range of LAIs, stand densities (450—4140 trees/ha) and illumination angles (32°—57°) under which it was tested

Regional-Scale Relationships of Leaf Area Index to Specific Leaf Area and Leaf Nitrogen Content

Specific leaf area (SLA) is an important link between vegetation water and carbon cycles because it describes the allocation of leaf biomass per unit of leaf area. Several studies in many vegetation types have shown that canopy SLA is closely related to canopy leaf nitrogen (N) content and photosynthetic capacity. SLA increases as light is attenuated by leaf area down through a plant canopy. It therefore follows that across an individual biome the spatial patterns in canopy—average SLA and leaf N content should be significantly correlated with the spatial patterns in leaf area index (LAI) and canopy transmittance. In this paper, we show that the LAI across the Oregon transect is closely related to canopy—average SLA (R2 = 0.82) and leaf N content on a mass basis (R2 = 0.80). Canopy—average leaf N per unit area is highly correlated to canopy transmittance (R2 = 0.94) across the transect. At any given site, canopy—average SLA and leaf N per unit area do not vary significantly, either seasonally or between different codominant species occupying the same site. The results of this study suggest that the spatial distribution of canopy—average SLA and leaf nitrogen content (and perhaps canopy photosynthetic capacity) can be predicted across biomes from satellite estimates of LAI

Developing Satellite-derived Estimates of Surface Moisture Status

Recent research has shown that the combination of spectral vegetation indices with thermal infrared observations may provide an effective method for parameterizing surface processes at large spatial scales. In this paper, we explore the remotely sensed surface temperature (Ts)/normalized difference vegetation index (NDVI) relationship regarding a) influence of biome type on the slope of Ts/NDVI, b) automating the definition of the relationship so that the surface moisture status can he compared with Ts/NDVI at continental scales. The analysis was carded out using 1) NOAA Advanced Very High Resolution Radiometer (AVHRR) data over a 300-km × 300-km area in western Montana under various land-use practices (grass, crops, and forests), 2) Earth Resources Observations Systems Data Center continental United States biweekly composite AVHRR data. A strong negative relationship was observed between NDVI and Ts over all biome types. The similarity of the Ts/NDVI relationships over different biomes indicated that fraction of vegetation cover has strong influence on the spatial variability of Ts. A substantial change in the Ts/NDVI relationship was observed over forests between wet and dry days. In comparison, no change was observed over irrigated crops. Results from the automated approach agreed well with those using manual selection. At continental scales, the slope of Ts/NDVI is strongly correlated to crop-moisture index values indicating that Ts/NDVI relation is sensitive to surface moisture conditions. Upon further development, this relationship may be useful for parameterizing surface moisture conditions in climate models, decomposition studies, and fire weather monitoring

Logical Step-Indexed Logical Relations

Appel and McAllester's "step-indexed" logical relations have proven to be a simple and effective technique for reasoning about programs in languages with semantically interesting types, such as general recursive types and general reference types. However, proofs using step-indexed models typically involve tedious, error-prone, and proof-obscuring step-index arithmetic, so it is important to develop clean, high-level, equational proof principles that avoid mention of step indices. In this paper, we show how to reason about binary step-indexed logical relations in an abstract and elegant way. Specifically, we define a logic LSLR, which is inspired by Plotkin and Abadi's logic for parametricity, but also supports recursively defined relations by means of the modal "later" operator from Appel, Melli\`es, Richards, and Vouillon's "very modal model" paper. We encode in LSLR a logical relation for reasoning relationally about programs in call-by-value System F extended with general recursive types. Using this logical relation, we derive a set of useful rules with which we can prove contextual equivalence and approximation results without counting steps

Monitoring Crop Evapotranspiration and Crop Coefficients over an Almond and Pistachio Orchard Throughout Remote Sensing

In California, water is a perennial concern. As competition for water resources increases due to growth in population, California’s tree nut farmers are committed to improving the efficiency of water used for food production. There is an imminent need to have reliable methods that provide information about the temporal and spatial variability of crop water requirements, which allow farmers to make irrigation decisions at field scale. This study focuses on estimating the actual evapotranspiration and crop coefficients of an almond and pistachio orchard located in Central Valley (California) during an entire growing season by combining a simple crop evapotranspiration model with remote sensing data. A dataset of the vegetation index NDVI derived from Landsat-8 was used to facilitate the estimation of the basal crop coefficient (Kcb), or potential crop water use. The soil water evaporation coefficient (Ke) was measured from microlysimeters. The water stress coefficient (Ks) was derived from airborne remotely sensed canopy thermal-based methods, using seasonal regressions between the crop water stress index (CWSI) and stem water potential (Ψstem). These regressions were statistically-significant for both crops, indicating clear seasonal differences in pistachios, but not in almonds. In almonds, the estimated maximum Kcb values ranged between 1.05 to 0.90, while for pistachios, it ranged between 0.89 to 0.80. The model indicated a difference of 97 mm in transpiration over the season between both crops. Soil evaporation accounted for an average of 16% and 13% of the total actual evapotranspiration for almonds and pistachios, respectively. Verification of the model-based daily crop evapotranspiration estimates was done using eddy-covariance and surface renewal data collected in the same orchards, yielding an R2 ≥ 0.7 and average root mean square errors (RMSE) of 0.74 and 0.91 mm·day−1 for almond and pistachio, respectively. It is concluded that the combination of crop evapotranspiration models with remotely-sensed data is helpful for upscaling irrigation information from plant to field scale and thus may be used by farmers for making day-to-day irrigation management decisions

Cosmic antiprotons as a probe for supersymmetric dark matter?

The flux of cosmic ray antiprotons from neutralino annihilations in the galactic halo is computed for a large sample of models in the MSSM (the Minimal Supersymmetric extension of the Standard Model). We also revisit the problem of estimating the background of low-energy cosmic ray induced secondary antiprotons, taking into account their subsequent interactions (and energy loss) and the presence of nuclei in the interstellar matter. We consider a two-zone diffusion model, with and without a galactic wind. We find that, given the uncertainties in the background predictions, there is no need for a primary (exotic) component to explain present data. However, allowing for a signal by playing with the uncertainties in the background estimate, we discuss the characteristic features of the supersymmetric models which give a satisfactory description of the data. We point out that in some cases the optimal kinetic energy to search for a signal from supersymmetric dark matter is above several GeV, rather than the traditional sub-GeV region. The large astrophysical uncertainties involved do not, one the other hand, allow the exclusion of any of the MSSM models we consider, on the basis of data. We present besides numerical results also convenient parameterizations of the antiproton yields of all `basic' two-body final states. We also give examples of the yield and differential energy spectrum for a set of supersymmetric models with high rates. We also remark that it is difficult to put a limit on the antiproton lifetime from present measurements, since the injection of antiprotons from neutralino annihilation can compensate the loss from decay.Comment: 22 pages, 11 figures, uses emulateapj.st

Biospheric Monitoring and Ecological Forecasting

The latest generation of NASA Earth Observing System (EOS) satellites has brought a new dimension to monitoring the living part of the Earth system - the biosphere. EOS data can now measure weekly global productivity of plants and ocean chlorophyll and of related biophysical factors, such as changes to land cover and to the rate of snowmelt. However, the greatest economic impact would be realized by forecasting biosphere conditions. This predictive ability would be an advanced decision-making tool used to mitigate dangers or to exploit positive trends

Generalized Toda Field Theories

In this paper we introduce a unified approach to Toda field theories which allows us to formulate the classes of $A_n$, $B_n$ and $C_n$ models as unique models involving an arbitrary continuous parameter $\nu$. For certain values of $\nu$, the model describes the standard Toda theories. For other values of $\nu$ it defines a class of models that involve infinitely many fields. These models interpolate between the various standard Toda field theories. They are conformally invariant and possess infinitely many conserved higher-spin currents thus making them candidates for a new set of integrable systems. A general construction is performed, which can effectively be used for the derivation of explicit forms of particular higher-spin currents. We also study the currents in a different representation in which they are linear in the dynamical variables having, however, a non-linear Poisson bracket algebra. An explicit formula for this Poisson structure is found.Comment: 35 pages, latex, no figures; submitted to Nucl. Phys.

Mapping Regional Forest Evapotranspiration and Photosynthesis by Coupling Satellite Data with Ecosystem Simulation

Mapping Regional Forest Evapotranspiration and Photosynthesis by Coupling Satellite Data With Ecosystem Simulatio