Airborne Imaging Spectrometer HySpex

The Remote Sensing Technology Institute (IMF) of the German Aerospace Center (DLR) operates an airborne imaging spectrometer system called HySpex. Owing to its accurate calibration, the system is well suited for benchmark reference measurements and feasibility studies for Earth observation applications. The sensor also serves as simulator for the upcoming German satellite mission EnMAP. HySpex covers the spectral range from the visible and near infrared (VNIR) to the short wave infrared (SWIR) and it has been extensively characterised with numerous measurements in the IMF calibration laboratory (CHB). The HySpex instrument is made available to interested third party users through the user service Optical Airborne Remote Sensing and Calibration Homebase (OpAiRS)

The CO2Image mission: retrieval studies and performance analysis

The CO2Image satellite mission, led by the German Aerospace Center (DLR), aims to demonstrate the feasibility of quantifying carbon dioxide (CO2) and methane (CH4) emissions from medium-size point sources. Several DLR institutes are currently working on the reliminary design phase (Phase B) of the mission. Here we present a performance analysis based on the current instrument specifications. The Beer InfraRed Retrieval Algorithm (BIRRA), the line-by-line radiative transfer model Py4CAtS (Python for Computational ATmospheric Spectroscopy) and a COSIS (Carbon dioxide Sensing Imaging Spectrometer) instrument model are employed to infer CO2 and CH4 concentrations from synthetic COSIS spectra. We evaluate the instrument's performance and determine if it meets the intended requirements. The study assesses uncertainties in the retrieved concentrations as well as errors in point source emission estimates caused by instrument noise. First results suggest that the detection and quantification limits stated in the mission requirements document are justified. The analysis also demonstrates that retrieval errors tend to increase when the signal-to-noise ratio is low, complicating the distinction between emission sources and background concentrations. Furthermore, we discuss non-instrumental effects and demonstrate that the fit quality significantly improves if a low-level plume is scaled instead of a background reference profile that covers the atmosphere's full vertical extent. The analysis on heterogeneous scenes (high albedo contrast) reveals that the various instrument setups perform similarly for both molecules

CO2 Image: The design of an imaging spectrometer for CO2 point source quantification

CO2Image is a satellite demonstration mission, now in Phase B, to be launched in 2026 by the German Aerospace Center (DLR). The satellite will carry a next generation imaging spectrometer for measuring atmospheric column concentrations of Carbon Dioxide (CO2). The instrument concept reconciles compact design with fine ground resolution (50-100 m) with decent spectral resolution (1.0-1.3 nm) in the shortwave infrared spectral range (2000 nm). Thus, CO2Image will enable quantification of point source CO2 emission rates of less than 1 MtCO2/a. This will complement global monitoring missions such as CO2M, which are less sensitive to point sources due to their coarser ground resolution and hyperspectral imagers, which suffer from spectroscopic interference errors that limit the quantification

CO2Image retrieval studies and performance analysis

Current and planned satellite missions such as the Japanese GOSAT (Greenhouse Gases Observing Satellite) and NASA's OCO (Orbiting Carbon Observatory) series and the upcoming Copernicus Carbon Dioxide Monitoring (CO2M) mission aim to constrain national and regional-scale emissions down to scales of urban agglomerations and large point sources. The CO2Image demonstrator mission of the German Aerospace Center (DLR) is specifically designed to detect and quantify carbon dioxide (CO2) and methane (CH4) emissions from medium-size point sources. To this end its COSIS (Carbon dioxide Sensing Imaging Spectrometer) push-broom grating spectrometer measures reflected solar radiation with a high spatial resolution of 50x50 m2, covering tiles of ~50x50 km2 extent. The instrument has a moderate spectral resolution of approximately ~1 nm and observes in a single spectral window in the 2 µm region. Here we present and discuss the impact of the expected COSIS performance on the retrieved level-2 data. The level-1 data (spectra) are generated using the Py4CAtS (Python for Computational ATmospheric Spectroscopy) line-by-line radiative transfer model and the COSIS SIMulator (COSIS-SIM). Based on the COSIS instrument parameters the analysis examines the retrieval errors related to noise which allows to estimate the detection and quantification limit of CO2 and CH4 emission rates at the instrument's spatial and spectral resolution. We further discuss the effect of heterogeneous scenes, i.e. high contrast surfaces that cause an effective distortion of the spectral response function by non-uniform illumination of the entrance slit. Finally, we assess the influence of initial guess values for the plume's vertical extent and shape on the retrieval

Vorbereitung, Validierung und Ergänzung der EnMAP Mission durch den Nutzerservice OpAiRS

Der Nutzerservice Optical Airborne Remote Sensing & Calibration Homebase (OpAiRS) betreibt flugzeuggetragene Sensoren für die optische Fernerkundung. Seine Leistungen stehen auch externen Nutzern aus Wissenschaft und Industrie im Rahmen von Kooperationsprojekten zur Verfügung. Mit dem seit dem Jahr 2007 nach ISO 9001 zertifizierten Service deckt das IMF in Kooperation mit dem DLR Flugbetrieb die gesamte Systemkette von der Aufnahme der Rohdaten bis zur Erzeugung höherwertiger Produkte (z.B. Orthobilder des Reflexionsgrades) ab: Planung, Organisation und Durchführung von Messkampagnen in Kooperation mit dem DLR Flugbetrieb Automatisierte Datenprozessierung mit der im IMF entwickelten Prozessierungsumgebung CATENA Kalibrierung der Daten & Korrektur von sensorspezifischen Artefakten (Keystone, Smile, Streulicht) auf Basis der Laborcharakterisierung in der Calibration Homebase (CHB) des IMF. Die Kalibrierung basiert auf denselben Verfahren, mit denen EnMAP in Kooperation mit OpAiRS Personal kalibriert wird. Atmosphärenkorrektur und Orthorektifizierung mit den im EOC entwickelten Werkzeugen Ortho und ATCOR Langzeitarchivierung der Daten im Deutschen Satellitendatenarchiv (D-SDA) des EOC Neben den flugzeuggetragenen Sensoren unterhält OpAiRS verschiedene Feldinstrumente, die zum einen für die Validierung der Flugzeugmessungen und zum anderen zur Unterstützung der Datenauswertung eingesetzt werden können. Die Expertise des IMF im Bereich der flugzeuggestützten optischen Fernerkundung basiert auf über 20 Jahren Erfahrung bei Entwicklung, Charakterisierung und Einsatz von abbildenden Spektrometern wie DAIS 7915, ROSIS oder HyMap. Der Nutzerservice OpAiRS setzt diese Tradition seit 2011 mit dem System HySpex (Fa. Norsk Elektro Optikk, NEO) konsequent fort. Nach einer zweijährigen Erprobungsphase mit aufwändigen Charakterisierungsmessungen in der CHB und bei der Physikalisch-Technischen Bundesanstalt (PTB) befindet sich das System seit 2014 im operationellen Betrieb. Die Kombination von HySpex mit einem hochauflösenden Luftbildkamerasystem (3K Kamera) erlaubt zudem die Entwicklung innovativer wissenschaftlicher Methoden der Datenfusion für die Erdbeobachtung. Insbesondere ist schon heute die Simulation von zukünftigen EnMAP Daten basierend auf flugzeuggestützten Messungen möglich

Flugzeuggestützte Fernerkundung am EOC

Überblick über die Expertise des EOC auf dem Gebiet der flugzeuggetragenen hyperspektralen Fernerkundung. Insbesondere wird das Angebot des Nutzerservice OpAiRS im Hinblick auf UAV & flugzeuggetragene Instrumente sowie die Kalibrierung derselben vorgestellt. Ein Schwerpunkt wird auf die Kapazitäten im Bereich radiometrische, spektrale und geometrische Kalibrierung von pushbroom Sensoren in der CHB gelegt

EnMAP related Cal/Val Activities of the User Service OpAiRS

The user service Optical Airborne Remote Sensing & Calibration Homebase (OpAiRS) operates airborne sensors for the development and validation of novel optical remote sensing applications. In close cooperation with DLR’s Research Flight Facilities the ISO certified entity offers expertise throughout the entire systems chain from flight planning via data acquisition to generation of value-added products. OpAiRS aims to provide high quality products with reliable uncertainties especially suited for challenging remote sensing applications and Cal/Val activities. Calibration has been at the focus of OpAiRS activities ever since its foundation and remains a topic of active research. For this purpose a laboratory especially dedicated to the calibration of push-broom sensors has been established and continuously expanded over the last decade. The Calibration Home Base for APEX (CHB) was partially funded by ESA for the calibration of the APEX instrument and is also used for the calibration of the OpAiRS sensor suite. The CHB has been a constant source of innovative methods for improved sensor characterization methods over the last few years. These methods have mainly been developed for the airborne hyperspectral sensor system HySpex acquired by DLR from the Norwegian company NEO in 2011. The same calibration techniques are also employed for the pre-flight calibration of the German earth observation satellite EnMAP in cooperation with the satellite manufacturer OHB. OpAiRS contributions include the concept for radiometric, geometric and spectral calibration of the instrument including a sophisticated stray light correction. The HySpex sensor system is very well suited for pre-launch simulation of EnMAP data and post-launch instrument validation, because the two instruments have similar characteristic properties and are both calibrated based on the same standards and methods developed in the CHB. The presentation will focus on current OpAiRS activities regarding calibration, validation and preparation of the EnMAP mission with HySpex and the CHB. Additionally we aim to present the OpAiRS capabilities for the calibration and validation of current and future satellite missions as a basis for potential cooperation

Transformation of point spread functions on an individual pixel scale

In some types of imaging systems, such as imaging spectrometers, the spectral and geometric pixel properties like center wavelength, center angle, response shape and resolution change rapidly between adjacent pixels. Image transformation techniques are required to either correct these effects or to compare images acquired by different systems. In this paper we present a novel image transformation method that allows to manipulate geometric and spectral properties of each pixel individually. The linear transformation employs a transformation matrix to associate every pixel of a target sensor $B$ with all related pixels of a source sensor $A$. The matrix is derived from the cross-correlations of all sensor $A$ pixels and cross-correlations of sensor $A$ and sensor $B$ pixels. We provide the mathematical background, discuss the propagation of uncertainty, demonstrate the use of the method in a case study, and show that the method is a generalization of the Wiener deconvolution filter. In the study, the transformation of images with random, non-uniform pixel properties to distortion-free images leads to errors that are one order of magnitude smaller than those obtained with a conventional approach