No abstract

1] Near-surface wind speeds (u) measured by terrestrial anemometers show declines (a 'stilling') at a range of midlatitude sites, but two gridded u datasets (a NCEP/NCAR reanalysis output and a surface-pressure-based u model) have not reproduced the stilling observed at Australian stations. We developed Australia-wide 0.01°resolution daily u grids by interpolating measurements from an expanded anemometer network for 1975 -2006. These new grids represented the magnitude and spatialvariability of observed u trends, whereas grids from reanalysis systems (NCEP/NCAR, NCEP/DOE and ERA40) essentially did not, even when minimising the sea-breeze impact. For these new grids, the Australianaveraged u trend for 1975 -2006 was À0.009 m s À1 a À1 (agreeing with earlier site-based studies) with stilling over 88% of the land-surface. This new dataset can be used in numerous environmental applications, including benchmarking general circulation models to improve the representation of key parameters that govern u estimation.

No abstract

The benefits of Hyperion hyperspectral data to agriculture have been studied at sites in the Coleambally Irrigation Area of Australia. Hyperion can provide effective measures of agricultural performance through the use of established spectral indexes if systematic and random noise is managed. The noise management strategy includes recognition of "bad" pixels, reducing the effects of vertical striping, and compensation for atmospheric effects in the data. It also aims to reduce compounding of these effects by image processing. As the noise structure is different for Hyperion's two spectrometers, noise reduction methods are best applied to each separately. Results show that a local destriping algorithm reduces striping noise without introducing unwanted effects in the image. They also show how data smoothing can clean the data and how careful selection of stable Hyperion bands can minimize residual atmospheric effects following atmospheric correction. Comparing hyperspectral indexes derived from Hyperion with the same indexes derived from ground-measured spectra allowed us to assess some of these impacts on the preprocessing options. It has been concluded that preprocessing, which includes fixing bad and outlier pixels, local destriping, atmospheric correction, and minimum noise fraction smoothing, provides improved results. If these or equivalent preprocessing steps are followed, it is feasible to develop a consistent and standardized time series of data that is compatible with field-scale and airborne measured indexes. Red-edge and leaf chlorophyll indexes based on the preprocessed data are shown to distinguish different levels of stress induced by water restrictions.

Many hydrological models engage spatially distributed measures of 'potential evapotranspiration' (ET pot ). The reliability and utility of the physically based PenmanMonteith approach to generate ET pot has been recently advocated. Assuming land-surface conditions, spatial surfaces of reference evapotranspiration (ET 0 ) can be generated taking into account the topographic influence of forcing meteorological variables. This was performed in this paper by spatially interpolating maximum (T max ) and minimum (T min ) air temperatures, wind speed (u) and vapor pressure (e a ), using a spline model with a linear sub-model dependency on elevation, and modelling the radiation environment, taking topography (i.e., elevation, slope and aspect) into account, prior to calculating ET 0 at each grid-cell. In accordance with previous research, resultant lapse rates showed a strong seasonal pattern; values were steeper in summer than winter and those for T max were steeper than for T min . Monthly mean T max lapse rates varied from À3.01°C km À1 in winter to À7.69°C km À1 in summer, with T min lapse rates ranging from À2.79°C km À1 in winter, to À6.64°C km À1 in summer. Monthly climatologies of the near-surface elevation-dependence (NSED) for u and e a also showed strong seasonal values. NSED of u varied from 2.01 ms À1 km À1 in winter reducing to 0.75 ms À1 km À1 in summer. The NSED for e a ranged from À0.08 kPa km À1 in winter to À0.64 kPa km À1 in summer. For a 252-month sequence from 1980 through 2000, spatial surfaces of ET 0 with a 100 m resolution for the 113,000 km 2 study site located in the Loess Plateau, China were generated using an 0022-1694/$ -see front matter ª a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j h y d r o lInterpolate-thencalculate; Calculate-theninterpolate 'interpolate-then-calculate' approach. Resultant ET 0 values varied from about 20 mm month À1 in winter to over 150 mm month À1 in summer. In order to assess the reliability of these ET 0 surfaces, pan evaporation (E pan ) was also spatially interpolated and from these a set of pan coefficient (K pan -a unitless ratio defined as ET 0 /E pan ) surfaces were calculated. Spatio-temporally averaged K pan values for the study site varied from 0.44 in April to 0.65 in late summer. K pan values were in agreement with another study using a Chinese 20 cm diameter micro-pan, and, as expected, were lower than other values documented using a Class A pan. The influence of topography, especially aspect, was seen on the resultant ET 0 and K pan , but not E pan , surfaces. Sensitivity analysis showed that results were particularly stable in the hydrologically active portion of the year extending from March to October, inclusive. This study demonstrated that high spatial resolution monthly surfaces of ET 0 can be spatially modelled while taking into account the influence of topography on the forcing variables. ª