Impacts of dichroic prism coatings on radiometry of the airborne imaging spectrometer APEX

The generation of well-calibrated radiometric measurements from imaging spectrometer data requires careful consideration of all influencing factors, as well as an instrument calibration based on a detailed sensor model. Deviations of ambient parameters (i.e., pressure, humidity, temperature) from standard laboratory conditions during airborne operations can lead to biases that should be accounted for and properly compensated by using dedicated instrument models. This study introduces a model for the airborne imaging spectrometer airborne prism experiment (APEX), describing the impact of spectral shifts as well as polarization effects on the radiometric system response due to changing ambient parameters. Key issues are related to changing properties of the dichroic coating applied to the dispersing elements within the optical path. We present a model based on discrete numerical simulations. With the improved modeling approach, we predict radiometric biases with an root mean square error (RMSE) below 1%, leading to a substantial improvement of radiometric stability and predictability of system behavior.

Evaluation of 3D surface scanners for skin documentation in forensic medicine: comparison of benchmark surfaces

Background

Two 3D surface scanners using collimated light patterns were evaluated in a new application domain: to document details of surfaces similar to the ones encountered in forensic skin pathology. Since these scanners have not been specifically designed for forensic skin pathology, we tested their performance under practical constraints in an application domain that is to be considered new.

Methods

Two solid benchmark objects containing relevant features were used to compare two 3D surface scanners: the ATOS-II (GOM, Germany) and the QTSculptor (Polygon Technology, Germany). Both scanners were used to capture and process data within a limited amount of time, whereas point-and-click editing was not allowed. We conducted (a) a qualitative appreciation of setup, handling and resulting 3D data, (b) an experimental subjective evaluation of matching 3D data versus photos of benchmark object regions by a number of 12 judges who were forced to state their preference for either of the two scanners, and (c) a quantitative characterization of both 3D data sets comparing 220 single surface areas with the real benchmark objects in order to determine the recognition rate's possible dependency on feature size and geometry.

Results

The QTSculptor generated significantly better 3D data in both qualitative tests (a, b) that we had conducted, possibly because of a higher lateral point resolution; statistical evaluation (c) showed that the QTSculptor-generated data allowed the discrimination of features as little as 0.3 mm, whereas ATOS-II-generated data allowed for discrimination of features sized not smaller than 1.2 mm.

Conclusion

It is particularly important to conduct specific benchmark tests if devices are brought into new application domains they were not specifically designed for; using a realistic test featuring forensic skin pathology features, QT Sculptor-generated data quantitatively exceeded manufacturer's specifications, whereas ATOS-II-generated data was within the limits of the manufacturer's specifications. When designing practically constrained specific tests, benchmark objects should be designed to contain features relevant for the application domain. As costs for 3D scanner hardware, software and data analysis can be hundred times as high compared to high-resolution digital photography equipment, independent user driven evaluation of such systems is paramount.

Index terms

Forensic pathology, Rough surfaces, Surface Scanning, Technology Assessment

Digital 3D reconstruction of two parahissian accessory bundles in a case of Wolff-Parkinson-White syndrome

Three-dimensional reconstruction of digitized histological serial sections of the cardiac conduction system yielded two accessory pathways in a case of a 24-day-old male infant who died after a short period of illness with ECG findings of Wolff-Parkinson-White syndrome. In infants, the differential diagnosis of possible accessory pathways connecting the AV conduction system, atrial or ventricular septum includes dispersed conduction system tissue without connecting features. This is why three-dimensional reconstruction is necessary in order to refute or establish connectivity of cell groups as found in histological serial slice images.

Modeling the noise equivalent radiance requirements of imaging spectrometers based on scientific applications

The derivation of radiometric specifications for imaging spectrometers from the visible to the short-wave infrared part of the spectrum is a task based on the requirements of potential scientific applications. A method for modeling the noise equivalent radiance at-sensor level is proposed. The model starts with surface reflectance signatures, transforms them to at-sensor signatures, and combines signatures of various applications with regard to performance requirements. The wavelength-dependent delta radiances are then derived at predefined radiance levels by use of a model of the sensor performance. The model is applied with regard to the upcoming Airborne Prism Experiment imaging spectrometer system. A combination of various potential application disciplines forms the basis of the experiment. The results help in the definition of radiometric levels for laboratory calibration of the noise equivalent radiance levels, the quantization of the signal, and the spectral range of an instrument to be designed.

Digital 3D image reconstruction of ventriculocapillary communication as revealed in one case after transmyocardial laser revascularization

TMR (Transmyocardial Laserrevascularization) was performed on the partially dyskinetic left ventricular anterior wall with stenotic coronary blood supply in a 61 year old woman with a history of angina and myocardial infarction. As an ischemic aneurysm developed in the anteroapical region of the TMR treated area, it became clear that TMR did not provide a substitute for coronary blood supply in this very heart region. The aneurysm was removed surgically 7 months after TMR and showed histopathologic features of an acute aneurysm. Three-dimensional image analysis helped prove the presence of linear tracks through several serial sections which were not easily visible in routine histology sections. Also, three-dimensional vessel reconstruction showed a connection between a small endocardial pit on one serial section with the capillary network in the adjacent serial sections. The results should not be generalized, as currently aneurysmectomy is an end point not reached by the majority of TMR-treated patients.