Signal Dependent Non-Linearity Calibration of an Imaging Spectrometer

We show the signal dependent non-linearity calibration of a HySpex VNIR-1600 hyperspectral sensor using the light addition method. The method has the advantage that a wide spectral range can be calibrated simultaneously with high accuracy. We developed a new setup that uses two lamps, which are coupled into an integrating sphere. The setup can illuminate the whole field of view simultaneously. Additionally, we enhanced the method to allow a denser sampling of the calibration curve than conventionally possible. The results show non-linearities up to 15% dependent on the detector area. After correction, the remaining error is negligible

LimnoVIS - A Robotic Surface Vehicle for Spectral Measurements in Inland Waters

Spectral measurements in aquatic remote sensing are usually carried out from ships, boats or stationary platforms. While the latter only covers a single location, mobile platforms can introduce significant errors due to unexpected movement (drift and rotation), reflection and shadowing effects from the ship’s hull, superstructures and the personnel conducting the measurements. To overcome these caveats, we developed the low-profile robotic platform LimnoVIS that can be operated autonomously or remotely controlled and is capable of keeping its position and orientation accurately through its omnidirectional maneuverability. The onboard measurement system comprises a VIS/NIR spectrometer (350-880 nm, 1 nm resolution) which is connected to four different optics via a fiber optical switch. This allows for rapid subsequent measurement of upwelling radiance above and under water, sky radiance and downwelling irradiance using reflectance standards or a cosine corrector, all by the same spectrometer. LimnoVIS carries also a profiler, which can be lowered by up to 30 m. It is equipped with a spectrometer and a tiltable diffusor for measuring benthic reflectance, LED and halogen lamps, a laser range finder, a camera, and sensors for temperature and pressure. Multiple onboard cameras with recording and live viewing capabilities are used for navigation, visual supervision and documentation of the measurements and for compiling shallow-water orthomosaics. Furthermore, LimnoVIS is equipped with a sonar for deriving bathymetry in the range of 0.5 to 30 m

ProGIRH-DLR: Remote sensing of water quality in the Mantaro River basin through spaceborne and ground-based acquisition of multi- and hyperspectral data

Peru is amongst the most affected countries by climate change in the world, with severe consequences on the availability of water across the country. The GIZ funded project "Multisectoral management of water resources in the Mantaro River basin" (ProGIRH) aims to improve the integrated and climate-sensitive water resource management in the Mantaro River basin. Within this framework, an IMF Team supports the Peruvian national water authority (ANA) in establishing remote sensing methodologies as a complement to traditional sampling-based water analysis. With a permanent focus on capacity building of the regional partners, the Team combines multi- and hyperspectral satellite imagery with in-situ spectral data, in order to define the possibilities and technical requirements necessary to establish a self-dependent and locally managed long-term observation of water quality and availability

Water quality monitoring in Térraba Sièrpe Wetland (Costa Rica) using multi- and hyperspectral EO data

The project MONEOWET focuses on multispectral and hyperspectral Earth Observation (EO) data to investigate water quality in relation to agricultural activities within the Térraba Sièrpe Wetland in Costa Rica. This study corresponds to an initiative focused on investigating the applicability of remote sensing data in tropical systems. The main topic of this project is the use of EO data to assess the impacts and dynamics of agricultural activities on the sensitive RAMSAR wetland ecosystem Térraba Sièrpe at the mouth of the Térraba and Sièrpe rivers. One goal of this project is to develop a first EO database and define analytical methods for water quality studies in that area and beyond. The results will provide a deeper insight into the processes of the entire wetland ecosystem and may help to detect harmful damage to the fragile environment caused by surrounding agricultural activities. The long-term goal is sustainable water and land use management that is exemplary for many other tropical wetlands in Latin America. Scientists from Germany and Costa Rica are working together to collect data with established (e.g. Sentinel 2, Landsat 8) and new Earth Observation sensors (e.g. DESIS on the ISS) to assess water quality parameters and link these parameters to agricultural land use in the surrounding area. The common goal of the project is to evaluate the applicability of Landsat 8, Sentinel-2 and DESIS multi- and hyperspectral satellite imagery for water quality studies in tropical environments. Field campaigns were carried out during wet season (November 2018 and November 2019) and dry season (March 2019 and March 2021). The sampling sites for in-situ measurements were taken in the three main meanders of the Sièrpe River and the main meander of Térraba River within the wetland. At each sampling site, the spectral signature of the river was recorded using an Ocean Optics Sensor System (OOSS). The multispectral (Sentinel 2, Landsat 8) and hyperspectral EO (DESIS) data were atmospherically corrected to Bottom-of-atmosphere (BOA) reflectance using Sen2cor (ESA) and PACO (Python-based Atmospheric Correction, DLR), respectively. The WASI-2D inversion method, a semi-analytical model, which retrieves the optically active water quality variables: chlorophyll, total suspended matter (TSM) and colored dissolved organic matter (CDOM) was used and parameterized with site - specific inherent optical properties (SIOPs) of the area and applied to time series of L2A Sentinel, Landsat 8 and DESIS images. Some of the Sentinel-2 and Landsat overpasses were coincident with available field data, however DESIS images could not be obtained during field campaigns, thus only a qualitative evaluation is presented. Although cloud cover in the tropics is a major challenge, the influence of thin clouds could be corrected and the concentrations of TSM and CDOM could be derived quantitatively. Chlorophyll could not be derived reliably in most areas, in particular not from Landsat 8, most likely because its concentration was relatively low and water absorption was dominated by CDOM. The high temporal dynamics of the river system, which is strongly influenced by tides, makes comparison of satellite data collected at different times very difficult, as is comparison with field data. Nevertheless, Sentinel 2-derived maps of water constituents and corresponding Landsat 8 and DESIS images show good agreements in the average concentrations of TSM and CDOM concentration and plausible spatial patterns, and field measurements show that they are in a plausible range. The results indicate that under favorable observational and environmental conditions, the applied atmospheric correction and the used retrieval algorithm are suitable to use DESIS, Sentinel 2 and Landsat 8 data for mapping TSM and CDOM in tropical environments, while chlorophyll is challenging. Their quantitative determination by satellite is therefore an important contribution of this project to the ecological assessment of the waters and the surrounding environment of the study area

Glioblastoma treated with magnetic resonance imaging-guided laser interstitial thermal therapy: Safety, efficacy, and outcomes

BACKGROUND: Despite the multitude of available treatments, glioblastoma (GBM) remains an aggressive and uniformly fatal tumor. Laser interstitial thermal therapy (LITT) is a novel, minimally invasive treatment that holds promise for treating patients with GBM who are not candidates for traditional open craniotomy. However, due to the recent introduction of LITT into clinical practice, large series that evaluate safety and long-term outcomes after LITT are lacking. OBJECTIVE: To present our institution\u27s series of over 50 GBM patients treated with LITT, with regard to safety, efficacy, and outcomes. METHODS: We performed a retrospective descriptive study of patients with histologically proven GBM who underwent LITT. Data collected included demographics, tumor location and volume, tumor genetic markers, treatment volume, perioperative complications, and long-term follow-up data. RESULTS: We performed 58 LITT treatments for GBM in 54 patients over 5.5 yr. Forty-one were recurrent tumors while 17 were frontline treatments. Forty GBMs were lobar in location, while 18 were in deep structures (thalamus, insula, corpus callosum). Average tumor volume was 12.5 ± 13.4 cm3. Average percentage of tumor treated with the yellow thermal damage threshold (TDT) line (dose equivalent of 43°C for 2 min) was 93.3% ± 10.6%, and with the blue TDT line (dose equivalent of 43°C for 10 min) was 88.0% ± 14.2%. There were 7 perioperative complications (12%) and 2 mortalities (3.4%). Median overall survival after LITT for the total cohort was 11.5 mo, and median progression-free survival 6.6 mo. CONCLUSION: LITT appears to be a safe and effective treatment for GBM in properly selected patients

Characterisation methods for the hyperspectral sensor HySpex at DLR’s calibration home base

The German Aerospace Center’s (DLR) Remote Sensing Technology Institute (IMF) operates a laboratory for the characterisation of imaging spectrometers. Originally designed as Calibration Home Base (CHB) for the imaging spectrometer APEX, the laboratory can be used to characterise nearly every airborne hyperspectral system. Characterisation methods will be demonstrated exemplarily with HySpex, an airborne imaging spectrometer system from Norsk Elektro Optikks A/S (NEO). Consisting of two separate devices (VNIR-1600 and SWIR-320me) the setup covers the spectral range from 400 nm to 2500 nm. Both airborne sensors have been characterised at NEO. This includes measurement of spectral and spatial resolution and misregistration, polarisation sensitivity, signal to noise ratios and the radiometric response. The same parameters have been examined at the CHB and were used to validate the NEO measurements. Additionally, the line spread functions (LSF) in across and along track direction and the spectral response functions (SRF) for certain detector pixels were measured. The high degree of lab automation allows the determination of the SRFs and LSFs for a large amount of sampling points. Despite this, the measurement of these functions for every detector element would be too time-consuming as typical detectors have 105 elements. But with enough sampling points it is possible to interpolate the attributes of the remaining pixels. The knowledge of these properties for every detector element allows the quantification of spectral and spatial misregistration (smile and keystone) and a better calibration of airborne data. Further laboratory measurements are used to validate the models for the spectral and spatial properties of the imaging spectrometers. Compared to the future German spaceborne hyperspectral Imager EnMAP, the HySpex sensors have the same or higher spectral and spatial resolution. Therefore, airborne data will be used to prepare for and validate the spaceborne system’s data

The Radiance Standard RASTA of DLR's calibration facility for airborne imaging spectrometers

The German Aerospace Center (DLR) operates the Calibation Home Base (CHB) as a facility for the calibration of airborne imaging spectrometers and for field spectrometers. Until recently, absolute radiometric calibration was based on an integrating sphere that is traceable to SI units through calibration at the German Metrology Institute PTB. However, the stability of the radiance output was not monitored regularly and reliably. This was the motivation to develop a new radiance standard (RASTA) which allows monitoring in the wavelength range from 380 to 2500 nm. Radiance source is a diffuse reflector illuminated by a tungsten halogen lamp. Five radiometers mounted in a special geometry are used for monitoring. This setup improves twofold the uncertainty assessment compared to the previously used integrating sphere. Firstly, lamp irradiance and panel reflectance have been calibrated at PTB additionally to the radiance of the complete system. This calibration redundancy allows to detect systematic errors and to reduce calibration uncertainty. Secondly, the five radiometers form a redundant control system to measure changes of the spectral radiance. This enables long-time monitoring of the radiance source including assessment of the uncertainty caused by aging processes. Further advantages concern the reduction of periods of non-availability, applicability to sensors with larger field of view, and the possibility to alter intensity and spectral shape in a well-known way by exchanging the reflector. RASTA has been calibrated at PTB in November 2011 in the wavelength range from 350 to 2500 n

DLR's New Traceable Radiance Standard “RASTA”

The German Aerospace Center (DLR) operates the Calibation Home Base (CHB) as a facility for the calibration of airborne imaging spectrometers such as APEX, HySpex and ROSIS, and for field spectrometers. Absolute radiometric calibration is performed so far using an integrating sphere that is traceable to SI units through calibration at the German Metrology Institute PTB. However, the stability of the radiance output is not monitored regularily and reliably since the small size (diameter 50 cm, exit port 20 cm x 4 cm) and the design make it difficult to install a device at a reproducible position which is suited to measure accurately changes of the spectral radiance. This drawback was the motivation to develop a new radiance standard (RASTA) which allows monitoring of small changes in the wavelength range from 380 to 2500 nm. The realisation is presented here

Konstruktion einer mechanischen Nachführung zur Bildstabilisierung einer Infrarotkamera

Zur Realisierung eines Wildretter-Systems für landwirtschaftliche Maschinen soll eine Infrarotkamera an einem Traktor installiert werden. Thermale Infrarotkamera-Systeme, die auf der Mikrobolometer-Technologie basieren benötigen eine lange Integrationszeit (ca. 10 ms). Bei der Aufnahme von Bildern während schneller Bewegungen entstehen daher Bildverschmierungen. Aufgabe dieser Diplomarbeit war es, ein mechanisches System zu entwickeln, welches die Bildverschmierung aufgrund der Fahrbewegung des Traktors durch Nachführung der Kamera kompensiert. Dazu wird ein Schrittmotor verwendet. Dieser schwenkt die Kamera abhängig vom Fahrtwegsignal des Traktors, um ihr Sichtfeld nachzuführen. Gesteuert wird das System von einem Mikrocontroller. Es wurde eine geeignete Steuerungselektronik entwickelt, und die nötigen Programme für den Mikrocontroller geschrieben. Um die Funktion im Labor überprüfen zu können, wurde ein geeigneter Labortest aufgebaut

Concept for improved radiometric calibration of radiance sources at the CHB facility

The Calibation Home Base (CHB) is a facility for the calibration of airborne imaging spectrometers such as APEX, ROSIS and in the future ARES, and for field spectrometers. Absolute radiometric calibration in the spectral range of 350–2500 nm is currently based on an integrating sphere whose spectral radiance was calibrated by the German National Metrology Institute PTB. However, a single radiance source cannot meet the requirements of a multitude of sensors, hence CHB operates several sources. In order to enable consistent calibration at CHB, a transfer radiometer based system will be used in the future. Detectors are much more stable than lamps, hence a well-designed system based on accurate detectors can reach much higher absolute accuracy of radiometric calibration than a lamp based set-up. The concept of this system, its hardware components and the expected accuracies are presented