Abstract. The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) is an imaging limb emission sounder operating in the thermal infrared region. It is designed to provide measurements of the upper troposphere/lower stratosphere with high spatial and high spectral resolution. The instrument consists of an imaging Fourier transform spectrometer integrated into a gimbal. The assembly can be mounted in the belly pod of the German High Altitude and Long Range research aircraft (HALO) and in instrument bays of the Russian M55 Geophysica. Measurements are made in two distinct modes: the chemistry mode emphasises chemical analysis with high spectral resolution, and the dynamics mode focuses on dynamical processes of the atmosphere with very high spatial resolution. In addition, the instrument allows tomographic analyses of air volumes. The first measurement campaigns have shown compliance with key performance and operational requirements.

Abstract-Ultrasound is frequently used to evaluate suspicious masses in breasts. These evaluations could be improved by taking advantage of advanced imaging algorithms, which become feasible for low frequencies if accurate knowledge about the phase and amplitude of the wave field illuminating the volume of interest is available. In this study, we compare five imaging and inversion methods: time-of-flight tomography, synthetic aperture focusing technique, backpropagation, Born inversion, and contrast source inversion. All methods are tested on the same full-wave synthetic data representing a 2-D scan using a circular array enclosing a cancerous breast submerged in water. Of the tested methods, only contrast source inversion yielded an accurate reconstruction of the speed-ofsound profile of the tumor and its surroundings, because only this method takes effects such as multiple scattering, refraction, and diffraction into account.I. Introduction U ltrasound breast imaging was shown to be successful in detecting tumors in dense breasts which may be missed using mammography [1], [2]. The application of ultrasound as a noninvasive imaging modality for breast cancer detection was already investigated in the seventies and eighties, and led to the development of ray-based cT [3]- [6] and doppler imaging methods [7] for breast cancer detection. In addition, hybrid methods and systems were developed which obtain pulse echo, attenuation, and speed-of-sound images simultaneously [8]. Taking advantage of these early successes, fully-automated ultrasound breast scanning systems were developed [9]- [13]. Typically, these systems allow for reproducible measurements when accurate knowledge about the scanning system and the field illuminating the volume of interest (phase and amplitude in absence of any contrast) is available. Having access to this information is an important condition for applying advanced 3-d imaging algorithms. although the early imaging methods are typically computationally efficient, they do not take into account many of the phenomena associated with the wave nature of the ultrasound field, e.g., diffraction, refraction, and multiple scattering. To overcome these limitations, various methods have been developed which do take into account (with varying degree) the (full-)wave nature of the field [14]- [19].This study aims to compare five different imaging methods-with varying complexity and underlying assumptions-for localizing and characterizing the tumor in a breast. Time-of-flight tomography (ToFT) is the only ray-based method investigated [20], [21]. With imaging, recorded travel times are related to a known matrix (containing information about the locations of all sources and receivers) and an unknown speed-of-sound map. This matrix-vector problem is successively solved using an iterative minimization algorithm [22], which uses total variation for regularization. The remaining four methods are wave-based. synthetic aperture focusing technique (saFT), also known in literature as migration or delayand-sum i...

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The paper is focused on sound-speed image reconstruction in 3-D ultrasound transmission tomography. Along with ultrasound reflectivity and the attenuation coefficient, sound speed is an important parameter which is related to the type and pathological state of the imaged tissue. This is important in the intended application, breast cancer diagnosis. In contrast to 2-D ultrasound transmission tomography systems, a 3-D system can provide an isotropic spatial resolution in the x-, y-, and z-directions in reconstructed 3-D images of ultrasound parameters. Several challenges must, however, be addressed for 3-D systems-namely, a sparse transducer distribution, low signal-to-noise ratio, and higher computational complexity. These issues are addressed in terms of sound-speed image reconstruction, using edge-preserving regularized algebraic reconstruction in combination with synthetic aperture focusing. The critical points of the implementation are also discussed, because they are crucial to enable a complete 3-D image reconstruction. The methods were tested on a synthetic data set and on data sets measured with the Karlsruhe 3-D ultrasound computer tomography (USCT) I prototype using phantoms. The sound-speed estimates in the reconstructed volumes agreed with the reference values. The breast-phantom outlines and the lesion-mimicking objects were also detectable in the resulting sound-speed volumes.

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