Because of their excellent performance capabilities, such as rapid response, high specificity and sensitivity, relatively compact size, low cost and easy operation, these biosensors can be a good alternative for the detection of vanadium [20].Alkaline phosphatases (ALPs), which catalyze the hydrolysis of phosphate esters, are widely distributed in mammalian tissues, and are present in high concentrations in bones, intestines, kidneys, placenta, and liver [21]. ALP is probably the most commonly used conjugated enzyme for immunoassays due to its high turnover number, broad substrate specificity and possibility of application. The determination of its activity has been carried out using various spectrophotometric and electrochemical methods [21�C25].

In the development of sensitive electrochemical ALP-based assays stable substrates such as phenyl phosphate [26�C28], naphthyl phosphate [28,29], ascorbic acid 2-phosphate [28,30], p-nitrophenyl phosphate [28,31] and rivoflavin-5-monophosphate [20] have been used. Among them, p-nitrophenyl phosphate is probably one of the most widely used substrate for ALP, since the enzymatically produced p-nitrophenol can be detected electrochemically [31].Reversible inhibition of ALP by vanadium has been previously reported [18,20,25], although this interaction has been scarcely used for vanadium determination [20]. The presence of vanadium produces a decrease of the chronoamperometric reduction signal registered that can be related to the concentration of this species.

Thus, the aim of this work has been the development of a screen-printed based amperometric biosensor, easily usable in any analytical laboratory, for the detection of vanadium. ALP has been cross-linked to the working electrode of screen-printed carbon electrodes (SPCEs) previously modified by gold nanoparticles (ALP-AuNPs-SPCEs). In order to obtain a biosensor with improved conductivity and performance for vanadium detection, AuNPs were deposited onto the working electrode previous to the enzyme immobilization [32]. The use of AuNPs have been reported in order to enhance the chronoamperometric Entinostat current response, yielding a sensor with an excellent electrocatalytic response, fast response time, long term stability and reproducibility [32�C38]. The ALP-based biosensor has been characterized for the detection of vanadium in water samples.

Figures of merit, such as precision or limit of detection, have been evaluated.2.?Results and DiscussionIn a previous paper 5-riboflavin monophosphate was used as a substrate for an alkaline phosphatase biosensor because there was no report of such a substrate being used for a biosensor. Preechaworapun [28] presented a list of the substrates for this type of enzymes, and Fanjul [31] studied the detection of p-nitrophenol in alkaline phosphatase assays.

The Shuttle Radar Technology Mission (SRTM) was used to gather data for digital elevation.New Millennium era: The new millennium era (Bailey et al., 2001) refers to highly advanced ��test-of concept�� satellites sent into orbit around the same time as EOS era, but the concepts 1|]# and ideas are different. These are basically satellites and sensors for the next generation. These include Earth Observing-1 carrying the first spaceborne hyperspectral data. The idea of Advanced Land Imager (ALI) as a cheaper, technologically better replacement for Landsat is also very attractive.Private industry era: The private industry era began at the end of the last millennium and beginning of this millennium (see Stoney, 2005).

This era consists of a number of innovations. First, collection of data in very high resolution (<10 meter).

This is typified by IKONOS and Quickbird satellites. Second, a revolutionary means of data collection. This is typified by Rapideye satellite constellation of 5 satellites, having almost daily coverage of any spot on earth at 6.5 meter resolution in 5 spectral bands including a red-edge band. Third, is the introduction of micro satellites, some under disaster monitoring constellation (DMC), which are designed and launched by surrey satellite technology Ltd. for Turkey, Nigeria, China, USGS, UK, and others. Fourth, is the innovation by Google Earth (http://earth.google.

com) in making rapid data access of VHRI for any part of the World through streaming technology that makes it easy for even a non-specialist to zoom and pan remote sensing data.Table 1.

Satellite sensor data characteristics1.2. Summary of sensors in environmental modelingA state-of-art of satellite sensors widely used in environmental applications and natural resources management are given in Table 1. These sensors provide data in a wide range of scales (or Batimastat pixel resolutions), radiometry, band numbers, and band widths and provides distinct advantage of consistency of data, synoptic coverage, global reach, cost per unit area, repeatability, precision, and accuracy. Added to this is the long-time series of archives and pathfinder datasets (e.g.

, Tucker, 2005, Agbu and James, 1994) that have global coverage. Much of this data is also free and accessible online.Many applications (e.g., Thenkabail et al., 2006) in environmental monitoring require frequent coverage of the same area. This can be maximized by using data from multiple sensors (Table 1). However, since data from these sensors are acquired Carfilzomib in multiple resolution (spatial, spectral, radiometric), multiple bandwidth, and in varying conditions, they need to be harmonized and synthesized before being used (Thenkabail et al., 2004).

Lower
Passive remote sensing has become a necessary tool for monitoring large scale processes. Remote sensing in the optical and thermal domain has been used to retrieve surface parameters such as thermal emissivity [1], leaf area index [2] and to map evapotranspiration [3].The accuracy in retrieved surface parameters is influenced by level of homogeneity of canopy and the pixel size of the images. Aggregation of the reflected/emitted radiation over large surfaces results in large errors for heterogeneous canopies [4�C5]. For example, the ASTER sensor has a nadir looking resolution of about 90 meters in the thermal spectrum [6]. The radiation emitted by the sub-pixel processes are then averaged to a singular value per pixel. This makes it impossible to understand these subpixel features if only images of one viewing angle are used.

Directional remote sensing has the potential to produce higher accuracy retrieval of surface parameters than nadir-only remote sensing [7�C8]. Reduction of signal to noise ratios (SNR) can be achieved by averaging multiple images and differences Dacomitinib in measured spectra for different viewing angles can be exploited [9]. It was shown by [10,11] that radiation reflected by a sparse canopy varies a great deal between oblique and nadir viewing angles. They were able to take advantage of these directional variations to retrieve with better precision the leaf area index.The use of optical directional imagery requires the knowledge of reflectance factors like the hemispherical-directional reflectance factor (HDRF) and the Bi-directional reflectance factor (BRDF).

Analogous to presented research it was shown [12] the requirement of knowledge on thermal directional signatures for thermal directional images. These directional signatures can be simulated using radiative transfer models like SAIL [13] and DART [14] or must be measured on ground.The directional viewing of the ground can be achieved using a goniometer [15,16]. Sensors like field spectrometers, [17] and thermal radiometers [18] can be attached to such a goniometer. A difficulty with most of the goniometric setups today is that they are non-automated and their operation is tedious and time-consuming. This causes a lot of problems when measuring thermal directional signatures.Thermal characteristics of vegetation are influenced by dynamic effects [5]. These dynamic effects consist of changing environmental parameters, like light intensity, sun angle and wind speed [19]. Underlying processes change with these temperatures.