FengYun-3C (FY-3C) is the second-generation polar-orbiting meteorological satellite in China. As one of the most important microwave payloads deployed onboard FY-3C, microwave radiation imager (MWRI) has been continuously observing radiance originating from land and sea surface and supports numerical weather predictions at regional and global scales. With a long-term monitoring of the cold-end reference, MWRI onboard FY-3C was found suffering from discontinuous observations due to its temporary power-OFF/power-ON in the years of 2015 and 2018, resulting in anomalous brightness temperature (TB) jump up to 2-3 K in magnitude at some channels. Analysis of the operating status of FY-3C MWRI indicated that deviation of the receiver system from its optimal operating status affects the nonlinearity characteristics significantly. A correction algorithm, which relates nonlinearity to the autogain control (AGC) operating voltage of the sensor, is thus proposed on the basis of on-ground thermal/vacuum (T/V) test results in the prelaunch phase in order to mitigate the calibration anomalies of FY-3C MWRI. Nonlinearity correction of FY-3C MWRI is further corroborated by comparisons of simultaneously overlapping observations of global precipitation measurement (GPM) microwave imager (GMI). The results demonstrated that after nonlinearity correction the performance of FY-3C MWRI has been improved at all channels except for the 36-V channel where technical failures have been detected since October 2016.

Microwave radiation imager (MWRI) is regarded as one of the most important microwave payloads on board China FengYun-3C Meteorological Satellite. The instrument suffers from calibration anomalies and exhibits observation- background (O-B) calibration bias difference between the ascending and descending passes at all channels (hereinafter AD bias). The calibration bias difference of MWRI between ascending and descending orbits hampers data assimilation in the numerical weather predictions and reanalysis systems. This paper proposes a physical-based correction algorithm for MWRI calibration, following a brief introduction to the calibration process of the instrument. The relationship between the observed brightness temperatures and the physical temperature of the hot load reflector is established to mitigate the intrusion of the emissive hot reflector at all channels which was not accurately estimated in the previous calibration process. Before- and after-correction comparisons using one-year observations show that the AD bias is effectively reduced, i.e., from ~2 K before correction to less than 0.2 K after correction, when rectifying the emissivity of the hot reflector in the calibration equation, whereas the change in the mean values of MWRI radiance is negligible.

This paper analyzes the effects of cloud supercooled liquid water (SCLW) on the polarization difference (PD) and brightness temperature (TB) generated by horizontally oriented snow particles at microwave band. Radiative transfer (RT) calculations from six realistic snowfall profiles selected from European Centre for Medium-Range Weather Forecasts (ECMWF) datasets indicate, that the existence of SCLW has noticeable impact on PD and TB at three window frequencies (150 GHz, 243 GHz and 664 GHz) for, respectively, light, median and heavy snowfall in dry and wet air conditions. It is implied that accurate information on liquid water is required to interpret polarimetric observations of ice clouds and snowfall for future satellite missions.

Reconstruction of the anterior cruciate ligament (ACL) through arthroscopy is one of the most common procedures in orthopaedics. It requires accurate alignment and drilling of the tibial and femoral tunnels through which the ligament graft is attached. Although commercial computer-assisted navigation systems exist to guide the placement of these tunnels, most of them are limited to a fixed pose without due consideration of dynamic factors involved in different knee flexion angles. This paper presents a new model for intraoperative guidance of arthroscopic ACL reconstruction with reduced error particularly in the ligament attachment area. The method uses 3D preoperative data at different flexion angles to build a subject-specific statistical model of knee pose. To circumvent the problem of limited training samples and ensure physically meaningful pose instantiation, homogeneous transformations between different poses and local-deformation finite element modelling are used to enlarge the training set. Subsequently, an anatomical geodesic flexion analysis is performed to extract the subject-specific flexion characteristics. The advantages of the method were also tested by detailed comparison to standard Principal Component Analysis (PCA), nonlinear PCA without training set enlargement, and other state-of-the-art articulated joint modelling methods. The method yielded sub-millimetre accuracy, demonstrating its potential clinical value.

This paper addresses the problem of fully-automatic localization and segmentation of 3D intervertebral discs (IVDs) from MR images. Our method contains two steps, where we first localize the center of each IVD, and then segment IVDs by classifying image pixels around each disc center as foreground (disc) or background. The disc localization is done by estimating the image displacements from a set of randomly sampled 3D image patches to the disc center. The image displacements are estimated by jointly optimizing the training and test displacement values in a data-driven way, where we take into consideration both the training data and the geometric constraint on the test image. After the disc centers are localized, we segment the discs by classifying image pixels around disc centers as background or foreground. The classification is done in a similar data-driven approach as we used for localization, but in this segmentation case we are aiming to estimate the foreground/background probability of each pixel instead of the image displacements. In addition, an extra neighborhood smooth constraint is introduced to enforce the local smoothness of the label field. Our method is validated on 3D T2-weighted turbo spin echo MR images of 35 patients from two different studies. Experiments show that compared to state of the art, our method achieves better or comparable results. Specifically, we achieve for localization a mean error of 1.6-2.0 mm, and for segmentation a mean Dice metric of 85%-88% and a mean surface distance of 1.3-1.4 mm.

Spaceborne D-InSAR system is a kind of SAR satellite system aiming at differential interferometry application. It provides us a capability of measuring subtle deformation on the ground with phase difference. In this work, we focused on the system performance analysis theory as a first step to launch the research work on the overall spaceborne D-InSAR system. After the theoretical model and major error analysis work, we realized that coherence is really important. The qualitative and quantitative analysis showed that the situation becomes worse due to volumetric and temporal decorrelations compared with single-pass InSAR system such as TanDEM-X system. The in-orbit SAR satellite data experiment study validated the quantitative analysis. In order to obtain high-precision D-InSAR measurement, there are some new problems to solve rather than just using an existing SAR satellite to implement D-InSAR.

We present a new run-time system that supports object sharing in a distributed system. The key insight in this system is that a handle-based implementation of such a system enables efficient and transparent sharing of data with both fine- and coarse-grained access patterns. In addition, it supports efficient execution of garbage-collected programs. In contrast, conventional distributed shared memory (DSM) systems are limited to providing only one granularity with good performance, and have experienced difficulty in efficiently supporting garbage collection. A safe language, in which no pointer arithmetic is allowed, can transparently be compiled into a handle-based system and constitutes its preferred mode of use. A programmer can also directly use a handle-based programming model that avoids pointer arithmetic on the handles, and achieve the same performance but without the programming benefits of a safe programming language. This new run-time system, DOSA (Distributed Object Sharing Architecture), provides a shared object space abstraction rather than a shared address space abstraction. The key to its efficiency is the observation that a handle-based distributed implementation permits VM-based access and modification detection without suffering false sharing for fine-grained access patterns. We compare DOSA to TreadMarks, a conventional DSM system that is efficient at handling coarse-grained sharing. The performance of fine-grained applications and garbage-collected applications is considerably better than in TreadMarks, and the performance of coarse-grained applications is nearly as good as in TreadMarks. Inasmuch as the performance of such applications is already good in TreadMarks, we consider this an acceptable performance penalty.

In this paper we describe a system for programming heterogeneous computing environments based upon Java and software distributed shared memory (DSM). Compared with existing approaches for heterogeneous computing, our system transparently handles both the hardware differences and the distributed nature of the system. It is therefore much easier to program. Java is a good candidate for heterogeneous programming because of its portability. Java provides the remote method invocation (RMI) mechanism for distributed computing. However, our early experience with RMI showed that the programmer must expend significant effort on such problems as data replication and the optimization of the remote interface to improve communication efficiency. Furthermore, the need for reference marshaling is not completely eliminated by RMI's effort to facilitate the sharing of linked structures between machines. A DSM system provides a shared memory abstraction over a group of physically distributed machines. It automatically handles data communication between machines and eliminates the need for the programmer to write message-passing code. A multithreaded Java program written for a single machine will require fewer changes to run on a Java/DSM combination than with RMI. We have been implementing a JDK-1.0.2 based parallel Java Virtual Machine on the TreadMarks DSM system. Our implementation includes a distributed garbage collector and supports the Java API with very few changes. In this paper we describe our motivation and the implementation, and report our early experience with programming under both RMI and DSM. © 1997 John Wiley & Sons, Ltd.

In this paper we present the design and implementation of a conservative garbage collection algorithm for distributed shared memory (DSM) applications that use weakly-typed languages like C or C++, and evaluate its performance. In the absence of language support to identify references, our algorithm constructed a conservative approximation of the set of cross-node references based on local information only. It was also designed to tolerate memory inconsistency on DSM systems that use relaxed consistency protocols. These techniques enabled every node to perform garbage collections without communicating with others, effectively avoiding the high cost of cross-node communication in networks of workstations. We measured the performance of our garbage collector against explicit programmer management using three application programs. In two out of the three programs the performance of the GC version is within 15% of the explicit version. The results showed that the garbage collector has two effects on application programs. On one hand, it tends to reduce memory locality, increasing the communication cost; on the other hand, it may eliminate synchronization and memory accesses that would be incurred if memory were managed by the programmer reducing the communication cost.