Stephen Hobbs

System Design for Geosynchronous Synthetic Aperture Radar Missions

Geosynchronous synthetic aperture radar (GEO SAR) has been studied for several decades but has not yet been implemented. This paper provides an overview of mission design, describing significant constraints (atmosphere, orbit, temporal stability of the surface and atmosphere, measurement physics, and radar performance) and then uses these to propose an approach to initial system design. The methodology encompasses all GEO SAR mission concepts proposed to date. Important classifications of missions are: 1) those that require atmospheric phase compensation to achieve their design spatial resolution; and 2) those that achieve full spatial resolution without phase compensation. Means of estimating the atmospheric phase screen are noted, including a novel measurement of the mean rate of change of the atmospheric phase delay, which GEO SAR enables. Candidate mission concepts are described. It seems likely that GEO SAR will be feasible in a wide range of situations, although extreme weather and unstable surfaces (e.g., water, tall vegetation) prevent 100% coverage. GEO SAR offers an exciting imaging capability that powerfully complements existing systems.

Radar Imaging From Geosynchronous Orbit: Temporal Decorrelation Aspects

Synthetic aperture radar imaging from geosynchronous orbit has significant potential advantages over conventional low-Earth orbit radars, but it also has challenges to overcome. The baseline mission we consider is an L-band geosynchronous passive (bistatic) radar achieving a spatial resolution of about 100 m with an integration time of 8 h. The atmosphere changes its structure on timescales of minutes to hours, and this has to be compensated if useful images are to be provided. The analysis shows that ionospheric delay is the major source of temporal decorrelation; other effects, such as tropospheric delay and Earth tides, have to be dealt with but appear to be easier to handle.

Dispersion of odour: a case study with a municipal solid waste landfill site in North London, United Kingdom

Municipal solid waste (MSW) landfills are a potential source of offensive odours that can create annoyance within communities. Dispersion modelling was used to quantify the potential odour strength causing an impact on the community around a particular MSW landfill site north of the London area in the United Kingdom. The case studies were completed with the short-term mode of COMPLEX-I, software developed by the US-EPA. The year 1998 was chosen as a source of baseline data. It was observed that by 2004, when the landfill will progress towards the west and a big band of the area towards the north would be partly/fully restored, the maximum contribution of the new sources giving higher odour concentrations would be in the southwesterly regions away from the landfill. Concentrations as high as 25.0 ou(E)/m(3) were observed with 3 min averaging time in the southwesterly areas as compared to concentrations of 20.0 ou(E)/m(3) at 10 min averaging times. However, the percentage frequency of such critical events occurring would be low. All other surrounding farms and small villages would be exposed to the concentration of 3.0 ou(E)/m(3) on certain occasions. In the year 2008, the majority of the filling fronts would be filled with wastes with no contributions from the active and operational cells. The maximum odour concentration around the landfill site for 1 h averaging time would be approximately 3 ou(E)/m(3) about 1.0 km north and 500 m west of the landfill site. For 3 min averaging time, the stretch of 5 ou(E)/m(3) band would be up to 2.5 km towards the north of the landfill site. It is argued that further analysis of the model calculations considering effects of wind direction, frequency of wind direction, stability of the atmosphere, selected odour threshold, integration time of the model, etc. would form a basis for calculating the separation distances of the landfill site from the surrounding community.

Odour from municipal solid waste (MSW) landfills: A study on the analysis of perception

The objective of this work was to develop a relationship between odour intensity and odour concentration by using data collected from various sensitive areas of the municipal solid waste (MSW) landfill site. A number of well-known psychophysical models (e.g., Weber-Fechner law, Stevens power law, Beidlers and Lafforts models) have been discussed that can successfully relate the perceived intensity with the odour concentration. Respective parameters for each of the models were estimated by the nonlinear Levenburg-Marquardt parameter estimation method. The overall performance of the model was tested statistically against sets of data from the olfactometry analysis. The model based on the Weber-Fechner law was ranked 1 in case of five out of nine samples and it has been found more representative of the less intense odour samples. The model based on Lafforts equation has represented the intensity-concentration relationship better with extremely low uncertainties on both parameters k1 and k2 for comparatively more intense odour samples.

Landfill odour: assessment of emissions by the flux footprint method

This paper will focus on the development of an innovative method for estimating odour fluxes and the contributing source areas from a Municipal Solid Waste (MSW) landfill site. A micrometeorological model has been developed based on the estimation of footprints of scalar odour concentration measurements in the atmospheric surface layer. The model is based on an analytical solution of the Eulerian advection-diffusion equation for vertical diffusion; model parameters include the location of the odour sensor and standard surface layer scaling factors. Lindvall Hoods are commonly used for measuring odour fluxes from ground based fugitive sources. However these cannot replicate the real atmospheric conditions. Common micrometeorological techniques for determining fluxes, such as vertical gradient measurements or eddy correlation methods, yield a flux magnitude but give practically no information about the source location. On the other hand the flux footprint describes the expansion and contraction of the required fetch under varying atmospheric stabilities. Preliminary results from the model are quite encouraging and agree well with those from Lindvall hood measurements. The accuracy of Lindvall hood measurements depends on how tightly the hood is positioned on the uneven landfill surface. It should prevent any air escaping out from the sides of the hood open to the atmosphere. Typical results show an average odour flux of ±25.91 (ou m−2 s−1) from freshly tipped wastes for an upwind fetch of 45.0 m and with the sensor at a height of 1.5 m from the ground. The hood results have a geometric mean of ±29.35 (ou m−2 s−1) based on the inlet air volume and a shade air temperature of 22.5 °C.

An airborne radar technique for studying insect migration

An airborne radar system able to measure insect density profiles and the orientation of individual insect targets was developed using standard components. Using the system, typical moth targets, with a radar cross-section of 1 cm 2 , can be detected to a range of about 1 km. Signals from 48 separate height bands, each 15 m deep, are recorded on three analogue data channels. Analogue outputs related to aerial population per hectare can be viewed in real-time. Signals recorded during recent field work show an inclined layer over a track length of 30 km, with target orientation profiles at two positions along the layer. The strongest orientation occurred in regions of wind shear. Airborne entomological radar powerfully complements existing techniques by virtue of its mobility, providing unique opportunities to study the spatial organization of migration, to track features as they develop and to survey large areas.

Woodland area estimation by spectral mixing: applying a goodness-of-fit solution method

Abstract A goodness-of-fit solution method for spectral mixture modelling is applied to Landsat Multi-Spectral Scanner (MSS) data. The modelled pixel proportions are compared against independent validation data obtained by aerial photographic interpretation. A goodness-of-fit parameter is found to provide an objective means of investigating the impact of both the number of ground-cover components and spatial averaging on the mixture solution.

Developments in Airborne Entomological Radar

Abstract Radar has been used to study insect flight for over 20 years. Radar, especially airborne radar, is unrivaled in its ability to observe the spatial organization of insect migration. This paper reports methods of data collection and analysis used by current airborne entomological radar systems and, in particular, the method used to review the data collected and visualize any large-scale structures detected. Examples of data from recent U.S. Department of Agriculture field experiments are presented to illustrate the analysis techniques. The data review method allows further data collection and analysis to be focused on areas of particular interest and thus significantly enhances the utility of airborne entomological radar.

Calibration and performance evaluation of a lightweight propellor anemometer for micrometeorological research

The results of calibrations of the airspeed measurement, distance constant and cosine response for a sensitive propellor (vane) anemometer are described. A triad of these anemometers may be used to measure wind velocity, and the estimated uncertainty in this measurement is evaluated for a typical triad and a range of wind directions.The propellor anemometers tested provide sensitivity similar to that of sonic anemometers for research, but at much lower cost (although for a narrower range of wind conditions). Large arrays of the anemometers allow the spatial and temporal structure of wind turbulence to be measured directly. The anemometers have been used for several years, and are robust enough for micrometeorological research.

Potential atmospheric and terrestrial aplications of a geosynchronous radar

We have identified 16 potential scientific applications of a SAR hosted by a geosynchronous satellite - a concept known as GeoSTARe - which would image much of Europe. These applications cover a very wide range of science including: meteorology, the cryosphere, geodetic geophysics, geohazards, flooding and agriculture. Large area coverage by L-band and localized coverage by X-band radars is required, using measurements from differential radar interferometry, interferometric coherence and backscatter intensity. The major advantage of these applications is the very high temporal frequency of observations achievable (a few tens of minutes).