Acute kidney injury (AKI) is a complex disorder for which currently there is no accepted definition. Having a uniform standard for diagnosing and classifying AKI would enhance our ability to manage these patients. Future clinical and translational research in AKI will require collaborative networks of investigators drawn from various disciplines, dissemination of information via multidisciplinary joint conferences and publications, and improved translation of knowledge from pre-clinical research. We describe an initiative to develop uniform standards for defining and classifying AKI and to establish a forum for multidisciplinary interaction to improve care for patients with or at risk for AKI. Members representing key societies in critical care and nephrology along with additional experts in adult and pediatric AKI participated in a two day conference in Amsterdam, The Netherlands, in September 2005 and were assigned to one of three workgroups. Each group's discussions formed the basis for draft recommendations that were later refined and improved during discussion with the larger group. Dissenting opinions were also noted. The final draft recommendations were circulated to all participants and subsequently agreed upon as the consensus recommendations for this report. Participating societies endorsed the recommendations and agreed to help disseminate the results. The term AKI is proposed to represent the entire spectrum of acute renal failure. Diagnostic criteria for AKI are proposed based on acute alterations in serum creatinine or urine output. A staging system for AKI which reflects quantitative changes in serum creatinine and urine output has been developed. We describe the formation of a multidisciplinary collaborative network focused on AKI. We have proposed uniform standards for diagnosing and classifying AKI which will need to be validated in future studies. The Acute Kidney Injury Network offers a mechanism for proceeding with efforts to improve patient outcomes.

Acute Kidney Injury Network: report of an initiative to improve outcomes in acute kidney injury

[1] The Shuttle Radar Topography Mission produced the most complete, highest-resolution digital elevation model of the Earth. The project was a joint endeavor of NASA, the National Geospatial-Intelligence Agency, and the German and Italian Space Agencies and flew in February 2000. It used dual radar antennas to acquire interferometric radar data, processed to digital topographic data at 1 arc sec resolution. Details of the development, flight operations, data processing, and products are provided for users of this revolutionary data set.

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The Shuttle Radar Topography Mission

On February 22, 2000 Space Shuttle Endeavour landed at Kennedy Space Center, completing the highly successful 11-day flight of the Shuttle Radar Topography Mission (SRTM). Onboard were over 300 high-density tapes containing data for the highest resolution, most complete digital topographic map of Earth ever made. SRTM is a cooperative project between NASA and the National Imagery and Mapping Agency (NIMA) of the U.S. Department of Defense. The mission was designed to use a single-pass radar interferometer to produce a digital elevation model (DEM) of the Earth's land surface between about 60 deg north and 56 deg south latitude. When completed, the DEM will have 30 m pixel spacing and about 15 m vertical accuracy. Two orthorectified image mosaics (one from the ascending passes with illumination from the southeast and one from descending passes with illumination from the southwest) will also be produced.

Synthetic aperture radar interferometry is an imaging technique for measuring the topography of a surface, its changes over time, and other changes in the detailed characteristic of the surface. By exploiting the phase of the coherent radar signal, interferometry has transformed radar remote sensing from a largely interpretive science to a quantitative tool, with applications in cartography, geodesy, land cover characterization, and natural hazards. This paper reviews the techniques of interferometry, systems and limitations, and applications in a rapidly growing area of science and engineering.

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Synthetic aperture radar interferometry

Geophysical applications of radar interferometry to measure changes in the Earth's surface have exploded in the early 1990s. This new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times. The resulting interferogram is a contour map of the change in distance between the ground and the radar instrument. These maps provide an unsurpassed spatial sampling density (∼100 pixels km−2), a competitive precision (∼1 cm), and a useful observation cadence (1 pass month−1). They record movements in the crust, perturbations in the atmosphere, dielectric modifications in the soil, and relief in the topography. They are also sensitive to technical effects, such as relative variations in the radar's trajectory or variations in its frequency standard. We describe how all these phenomena contribute to an interferogram. Then a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments, including the four satellites currently in orbit: ERS-1, ERS-2, JERS-1, and RADARSAT. The next chapter suggests some guidelines for interpreting an interferogram as a geophysical measurement: respecting the limits of the technique, assessing its uncertainty, recognizing artifacts, and discriminating different types of signal. We then review the geophysical applications published to date, most of which study deformation related to earthquakes, volcanoes, and glaciers using ERS-1 data. We also show examples of monitoring natural hazards and environmental alterations related to landslides, subsidence, and agriculture. In addition, we consider subtler geophysical signals such as postseismic relaxation, tidal loading of coastal areas, and interseismic strain accumulation. We conclude with our perspectives on the future of radar interferometry. The objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intuition necessary to interpret it.

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Radar interferometry and its application to changes in the Earth's surface

Presented is a new solution for real-time motion compen- sation. The main idea is to extract all the necessary motions of the aircraft from the radar backscatter signal using a new radar configu- ration and new methods for evaluating the azimuth spectra of the ra- dar signal. Hence an inertial navigation system becomes unnecessary for many applications. The motion compensation parameters for real- time motion error correction are the range delay, the range dependent phaseshift, and the pulse repetition frequency. The motions of the air- craft to be extracted are the displacement in line-of-sight (LOS) direc- tion, the aircraft's yaw and drift angle, and the forward velocity. Re- sults show that a three-look image with an azimuth resolution of 3 m in L-band using a small aircraft is achievable, and the implementation of this method in real time using an array processor is feasible. YNTHETIC APERTURE RADARS (SAR) synthe- S size a long antenna by transmitting electromagnetic energy and coherently adding the successively reflected and received pulses to obtain high resolution in flight (azi- muth) direction. The resolution in range direction is achieved either by transmitting very short pulses or by using pulse compression. To achieve a coherent integra- tion, called azimuth compression, it is necessary that phase errors, resulting from spurious platform motion er- rors, are compensated. The platform motion error is de- fined as the error between the actual flight path and the nominal one. For SAR systems mounted on small air- crafts, motion errors are considerably high due to atmo- spheric turbulence and aircraft properties. After having determined the motion errors of the aircraft, motion com- pensation can be realized by adjusting the pulse repetition frequency (PRF) , applying a range-dependent phaseshift to each received pulse and delaying it. By adjusting the PRF, one compensates for the aircraft fonvard-velocity variations, so that the emissions will occur at constantly spaced intervals. Adjusting the phase and range delay, one compensates for the displacement in line-of-sight (LOS) direction. This paper will present a method to extract the displace- ment in LOS-direction, the aircraft velocity, and the yaw and drift angle from the radar raw data. The method is based on the analysis of the azimuth spectrum of the radar

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A New Method Of Aircraft Motion Error Extraction From Radar Raw Data For Real Time Motion Compensation

The authors exploit the interferometric multifrequency potentiality of the SIR-C/X-SAR system which is equipped with an L-, C-, and X-band sensor. They present a solution to improve the unwrapping performance of the C- and X-band data by considering the L-band unwrapped pattern. A new algorithm for the generation of a single digital elevation model (DEM) combining L-, C-, and X-band information is presented. This solution is based on the fusion of the unwrapped phase patterns by using a Kalman filter. The proposed fusion operation also accounts for the coherence characteristics of the three data sets. The selected test site is the Mt. Etna region in Italy which is very interesting from the volcanological and geological point of view. Numerical assessments of the achieved results are provided by evaluating the height accuracy with respect to a reference DEM.

Generation of digital elevation models by using SIR-C/X-SAR multifrequency two-pass interferometry: the Etna case study

Repeat-pass interferometry data were acquired during the first and second SIR-C/X-SAR missions in April and October 1994. This paper presents the first results from X-SAR interferometry at four different sites. The temporal separations were one day and six months. At two sites the coherence requirements were met, resulting in high quality interferograms. A digital elevation model in ground range geometry has been derived. The limitations of the X-SAR interferometry are discussed. >

X-SAR interferometry: first results

A new method for moving target detection, localization, and velocity estimation using SAR raw data is presented which allows the determination of the target's complete velocity vector. The method is applicable if the target has either a tangential velocity (/spl mu//sub T//spl ne/0) or a radial acceleration (/spl nu//spl dot//sub R//spl ne/0), or both. It is based on the analysis of the Doppler rate map which is obtained from the range compressed raw data, applying the reflectivity displacement method (RDM). The tangential velocity of each moving target is obtained from its own Doppler rate and the radial velocity from its own linear range migration. A velocity accuracy better than 3 m/s can be achieved for the airborne case. The method is validated experimentally by the use of real SAR data obtained by DLR's E-SAR. The paper gives a short description of the state of the art of moving target velocity measurements, introduces the RDM for stationary targets and its extension to the application for moving targets. It furthermore shows experimental results. >

A new MTI-SAR approach using the reflectivity displacement method

This paper describes how high-precision digital elevation models (DEMs) are obtained over the Wadden Sea using the AeS-1 airborne interferometric radar. The Wadden Sea is an intertidal zone along the coast having height variations less than 5 m over 30 km and is free of vegetation. The resulting DEM has a grid spacing of 2.5 m and an absolute height accuracy of 5 cm root mean square (rms), as verified by theodolite measurements. This paper describes the radar system, the processing techniques, the test area, the results, and the verification procedure.

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Joao Moreira

Papers

A New Method Of Aircraft Motion Error Extraction From Radar Raw Data For Real Time Motion Compensation

Generation of digital elevation models by using SIR-C/X-SAR multifrequency two-pass interferometry: the Etna case study

X-SAR interferometry: first results

A new MTI-SAR approach using the reflectivity displacement method

Generation of high precision DEMs of the Wadden Sea with airborne interferometric SAR