Christian Brommer

Bio

I am currently a Ph.D. candidate at the University of Klagenfurt (AAU) in the Department of “Control of Networked Systems” (CNS), Austria. My research is focused on the field of robot localization and modular Multi-Sensor-Fusion.

My interest in this field began during my stay as an intern and volunteer at the NASA Jet Propulsion Laboratory (JPL), where I worked on the implementation of a Multi-Sensor-Fusion framework and autonomous vehicle projects such as a Tandem Micro Air Vehicle System for Joint 3D Terrain Reconstruction. My interests also include Embedded Systems, Robotics, Multi-Vehicle Interaction, and Autonomous Systems.

Publications

Journals

INSANE: Cross-Domain UAV Data Sets with Increased Number of Sensors for developing Advanced and Novel Estimators - Under review
Authors:
Christian Brommer, Alessandro Fornasier, Martin Scheiber, Jeff Delaune, Roland Brockers, Jan Steinbrener, and Stephan Weiss
Publisher:
International Journal of Robotics Research (IJRR)
Year:
February 2023

The INSANE data sets are a versatile collection of Micro Aerial Vehicle (MAV) data sets designed to support research in autonomous robotic platforms. Accurate and robust localization is a key requirement for these platforms to navigate safely in various dynamic environments. The data sets provide different scenarios with multiple levels of difficulty for localization methods, including indoor and outdoor environments and challenging Mars analog scenarios. The extensive sensor suite includes various sensor categories, such as multiple Inertial Measurement Units (IMUs) and cameras, and each data set provides highly accurate ground truth. The data sets and post-processing tools are available for download and aim to reflect real-world scenarios and sensor effects to support research on machine learning-based sensor signal enhancement methods for improved localization.

Overcoming Bias: Equivariant Filter Design for Biased Attitude Estimation with Online Calibration
Authors:
Alessandro Fornasier, Yonhon Ng, Christian Brommer, Christoph Böhm, Robert Mahony and Stephan Weiss
Publisher:
IEEE Robotics and Automation Letters (RA-L)
Year:
October 2022

This letter presents a new generic formulation for a gyroscope aided attitude estimator using N direction measurements. The approach incorporates navigation, extrinsic calibration for all direction sensors, and gyroscope bias states in a single geometric structure. The proposed filter-based estimator improves the transient response, and the asymptotic bias and extrinsic calibration estimation compared to state-of-the-art approaches. The estimator is verified in simulations and tested in real-world experiments.

CNS Flight Stack for Reproducible, Customizable, and Fully Autonomous Applications
Authors:
Martin Scheiber, Alessandro Fornasier, Roland Jung, Christoph Böhm, Rohit Dhakate, Christian Stewart, Jan Steinbrener, Stephan Weiss, and Christian Brommer
Publisher:
IEEE Robotics and Automation Letters (RA-L)
Year:
February 2022

This research paper presents the CNS Flight Stack, a high-level flight stack for unmanned aerial vehicles (UAVs) designed to enable safe and fully autonomous long-duration missions. The framework is platform-agnostic, uses low compute complexity, and can be extended with other sensor modalities, integrity checks, and mission modules. The CNS Flight Stack has been tested in over 450 real-world flights, making it a valuable tool for the UAV community, and it is freely available for external mission planners and localization modules.

MaRS: A Modular and Robust Sensor-Fusion Framework
Authors:
Christian Brommer, Roland Jung, Jan Steinbrener, and Stephan Weiss
Publisher:
IEEE Robotics and Automation Letters (RA-L)
Year:
December 2020

This research paper presents a modular sensor-fusion framework that allows for the addition and removal of sensors during runtime in dynamic environments. The framework handles system and sensor initialization, measurement updates, and switching of asynchronous multi-rate sensor information with sensor self-calibration. It also has the ability to handle delayed measurements, out-of-sequence updates, and monitor sensor health. The introduced true-modularity is based on covariance segmentation, allowing the processing of propagation and updates on a per-sensor basis. The framework was tested in a precision landing scenario using GNSS, barometer, and vision measurements in both simulation and real-world scenarios. The framework is open-sourced and available for the community to use.

AMADEE-18: Vision-based unmanned aerial vehicle navigation for Analog Mars Mission (AVI-NAV)
Authors:
Eren Allak, Christian Brommer, Diego Dallenbach, and Stephan Weiss
Publisher:
Astrobiology - Mary Ann Liebert, Inc.
Year:
November 2020

In the context of the AMADEE-18 analog Mars mission, a team of researchers focused on testing the localization of an unmanned aerial vehicle (UAV) on Mars. Due to the computational limitations of robot helicopters, accurate localization is crucial for autonomous navigation and path planning. In the absence of a global positioning system, the team tested a visual-inertial odometry (VIO) algorithm and camera in a Mars-like analog environment to evaluate its feasibility for localization on Mars. Flight datasets from various terrains were used to challenge the functionality of the VIO algorithm and provide insights into the desired surface structure, texture, and mission times for surface relative navigation of UAVs on Mars. The study provides valuable information for the challenges associated with human-based exploration of the Red Planet.

Long‐duration fully autonomous operation of rotorcraft unmanned aerial systems for remote‐sensing data acquisition
Authors:
Danylo Malyuta, Christian Brommer, Daniel Hentzen, Thomas Stastny, Roland Siegwart, and Roland Brockers
Publisher:
Journal of Field Robotics (JFR)
Year:
February 2020

Introducing our fully autonomous rotorcraft unmanned aerial system (UAS) - the solution to long-term observation missions in remote locations without any human intervention. With limited flight times of traditional UAS and the need for humans in the loop, our platform offers a solution for uninterrupted operations over days or weeks. Our technology addresses two critical areas: platform autonomy and vision-based precision landing for automated energy replenishment. Our high-level autonomous decision-making hierarchy and vision-based landing system uses AprilTag fiducials to estimate landing pad pose for accuracy. We have conducted indoor and outdoor experiments, where the UAS executed 16, 48, and 22 flights with a flying-to-charging ratio of 1 to 10. With no human interaction required, this is the first quadrotor system to operate long-term outdoors.

Conferences

Revisiting Multi-GNSS Navigation for UAVs - An Equivariant Filtering Approach
Authors:
Martin Scheiber, Alessandro Fornasier, Christian Brommer, and Stephan Weiss
Publisher:
International Conference on Advanced Robotics (ICAR 2023)
Year:
October 2023

This study introduces equivariant filtering as a powerful tool for refining state estimation in unmanned aerial vehicles (UAVs). Equivariant filters offer faster convergence rates and greater robustness to initial state errors compared to traditional methods by exploiting mathematical symmetries. The research demonstrates their effectiveness in sensor fusion using GNSS and IMU data and validates their practicality in real-world scenarios with the INSANE Dataset. This innovation holds immense promise for enhancing UAV state estimation in real-world environments.

AI-Based Multi-Object Relative State Estimation with Self-Calibration Capabilities
Authors:
Thomas Jantos, Christian Brommer, Eren Allak, Stephan Weiss, and Jan Steinbrener
Publisher:
2023 IEEE International Conference on Robotics and Automation (ICRA)
Year:
February 2023

This paper highlights the importance of extracting meaningful information from sensory data in mobile robotics. It introduces a method that combines AI-based object pose estimation from images with inertial measurement unit (IMU) data. This fusion enables accurate multi-object relative state estimation in a 6-DoF context, demonstrated through real-world experiments. The approach’s self-calibrating capabilities ensure reliable and reproducible results.

Multi-State Tightly-Coupled EKF-Based Radar-Inertial Odometry With Persistent Landmarks
Authors:
Jan Michalczyk, Roland Jung, Christian Brommer, and Stephan Weiss
Publisher:
2023 IEEE International Conference on Robotics and Automation (ICRA)
Year:
February 2023

This paper presents a Radar-Inertial Odometry (RIO) method that leverages advanced techniques from vision research to accurately estimate a robot’s position and velocity using radar data. The approach combines past robot poses, radar measurements, and Inertial Measurement Unit (IMU) readings in an Extended Kalman Filter (EKF) framework. This method is particularly valuable for Unmanned Aerial Vehicles (UAVs) operating in challenging environments without GNSS, and demonstrates its effectiveness in real flight experiments.

Modular Multi-Sensor Fusion for Underwater Localization for Autonomous ROV Operations
Authors:
Martin Scheiber, Alexandre Cardaillac, Christian Brommer, Stephan Weiss and Martin Ludvigsen
Publisher:
IEEE OCEANS22
Year:
October 2022

This article discusses the challenges of localization filters for underwater vehicles and presents the Modular and Robust Sensor-Fusion Framework (MaRS) as a solution. MaRS is extended to work with underwater vehicles and their environment and allows efficient use of asynchronous sensors, handles measurement outliers and outages, and includes sensor-frame initialization and online extrinsic calibration methods. Tests using a small remotely operated vehicle (ROV) show improved handling of sensors and state estimation results in real harbor-like environments.

Autonomous Control Of Redundant Hydraulic Manipulator using Reinforcement Learning with Action Feedback
Authors:
Rohit Dhakate, Christian Brommer, Harald Gietler, Stephan Weiss, and Jan Steinbrener
Publisher:
IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)
Year:
July 2022

This article describes a data-driven approach to autonomously control hydraulic manipulators with minimal system information. The hydraulic actuation dynamics are modeled using actuator networks, which emulates the real system in a simulation environment. The approach uses a neural network control policy based on end-effector position tracking learned through Reinforcement Learning (RL) with Ornstein-Uhlenbeck process noise for efficient exploration. The proposed approach is implemented on a hydraulic forwarder crane to track the desired position of the end-effector in 3D space, and the results demonstrate the feasibility of deploying the learned controller directly on the real system.

Kinematics-Inertial Fusion for Localization of a 4-Cable Underactuated Suspended Robot Considering Cable Sag
Authors:
Eren Allak, Rooholla Khorrambakht, Christian Brommer and Stephan Weiss
Publisher:
IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)
Year:
July 2022

This article discusses the challenges of estimating the end-effector pose for Suspended Cable-Driven Parallel Robots (SCDPR), due to the curved shape of cables known as cable sag. The proposed real-time pose estimation algorithm considers cable sag to reduce estimation errors and also employs an Inertial Measurement Unit (IMU) to improve accuracy for dynamic motion. The approach reduces Root Mean Squared Error (RMSE) compared to standard methods and is evaluated on a real system with ground truth pose information.

Combined System Identification and State Estimation for a Quadrotor UAV
Authors:
Christoph Böhm, Christian Brommer, Alexander Hardt-Stremayr, and Stephan Weiss
Publisher:
IEEE International Conference on Robotics and Automation (ICRA)
Year:
May 2021

This paper proposes a probabilistic approach for online system identification and self-calibration in small rotorcraft Unmanned Aerial Vehicles (UAVs) for improved control design and navigation. The approach integrates the system identification and state estimation processes into a single framework, allowing for self-awareness and self-healing, and uses a combination of inertial cues, dynamic modeling, and an additional sensor for convergence to the optimal value. The results are supported by simulations using realistic data in Gazebo.

Improved State Propagation through AI-based Pre-processing and Down-sampling of High-Speed Inertial Data
Authors:
Jan Steinbrener, Christian Brommer, Thomas Jantos, Alessandro. Fornasier, and Stephan Weiss
Publisher:
IEEE International Conference on Robotics and Automation (ICRA)
Year:
February 2021

This paper introduces a new approach to improve state propagation for unmanned aerial vehicles using AI algorithms to preprocess high-speed inertial data. Two network architectures are evaluated, an LSTM-based approach and a Transformer encoder architecture, with the former outperforming the latter. The networks are designed to directly accept input data at variable rates and provide sufficient temporal history for good performance while maintaining a high propagation rate of preprocessed IMU samples. Results show significant improvements in propagation error even for long IMU propagation times.

Improved state estimation in distorted magnetic fields
Authors:
Christian Brommer, Christoph Böhm, Jan Steinbrener, Roland Brockers, and Stephan Weiss.
Publisher:
International Conference on Unmanned Aircraft Systems (ICUAS)
Year:
September 2020

In this paper, we propose a method to address the performance loss or failure of state estimation and navigation frameworks caused by local magnetic distortions. The use of magnetometers on-board mobile platforms suffer from these issues if magnetic distortions are not detected and mitigated. The paper shows the importance of representing magnetic variation in a spherical coordinate system instead of Cartesian coordinates, which can improve estimator consistency and enable accurate and fast mitigation of magnetic disturbances. The approach is validated by performing tests with simulated and real-world data on embedded hardware. The proposed method has the potential to lead to better system state estimates in magnetically distorted areas.

Decentralized Collaborative State Estimation for Aided Inertial Navigation
Authors:
Roland Jung, Christian Brommer, and Stephan Weiss.
Publisher:
IEEE International Conference on Robotics and Automation (ICRA)
Year:
May 2020

This paper introduces a new approach to filtering data from sensors on multiple autonomous agents, such as robots or drones, to estimate the agents’ positions and orientations relative to each other. The proposed method, called Quaternion-based Error-State Extended Kalman Filter (Q-ESEKF), uses advanced mathematical techniques to make the filtering more accurate and efficient. It also incorporates Collaborative State Estimation (CSE), which allows each agent to estimate its own state independently while taking into account measurements from other agents. The paper presents simulation results demonstrating the effectiveness of the approach on two benchmark datasets in 3D.

Long-Duration Autonomy for Small Rotorcraft UAS including Recharging
Authors:
Christian Brommer, Danylo Malyuta, Daniel Hentzen, and Roland Brockers
Publisher:
IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)
Year:
October 2018

This research proposes a fully autonomous small rotorcraft UAS for long-term observation missions that requires no human intervention. The system addresses two key technologies critical for such a system: full platform autonomy and vision-based precision landing for automated energy replenishment. Experimental results show up to 11 hours of fully autonomous operation in indoor and outdoor environments, demonstrating the system’s capability. This technology could revolutionize unmanned aerial vehicle surveillance and monitoring applications, enabling observations at precise locations over long periods of time without the need for human intervention.

Workshops

AMADEE-20 Exploration Cascade using Robotic Vehicles
Authors:
Christian Brommer, Alessandro Fornasier, Stefanie Garnitschnig, Gernot Grömer, Sophie Gruber, Paolo Guardabasso, Richard Halatschek, Vittorio Netti, Keerthi D Ramanna, Gerald Steinbauer, and Stephan Weiss
Publisher:
IROS Workshop on Planetary Exploration Robots: Challenges and Opportunities
Year:
October 2020

The extended abstract presents the AMAZE helicopter as part of the robotic team involved in the exploration cascade of the Mars Analog Simulation AMADEE-20. Analog research is used to prepare and train for future Mars exploration missions, with the Austrian Space Forum (OeWF) having conducted 12 Mars analog missions as part of the AMADEE research program. The AMADEE program develops strategies to detect life on extraterrestrial planets and ensures high fidelity for all OeWF analog missions. The AMAZE helicopter will be used for surface exploration during the simulation in the Ramon Crater, Negev Desert, Israel, which aims to replicate conditions on Mars.

Patents

Long-Duration, Fully Autonomous Operation of Rotorcraft Unmanned Aerial Systems Including Energy Replenishment

A method and system provide the ability to autonomously operate an unmanned aerial system (UAS) over long durations of time. The UAS vehicle autonomously takes off from a take-off landing-charging station and autonomously executes a mission. The mission includes data acquisition instructions in a defined observation area. Upon mission completion, the UAS autonomously travels to a target landing-charging station and performs an autonomous precision landing on the target landing-charging station. The UAS autonomously re-charges via the target landing-charging station. Once re-charged, the UAS is ready to execute a next sortie. When landed, the UAS autonomously transmits mission data to the landing-charging station for in situ or cloud-based data processing.

  • Date: January 9, 2024
  • Authors: Roland Brockers, Stephan Weiss, Danylo Malyuta, Christian Brommer, Daniel Robert Hentzen
  • Patent Number: US 11866198
  • Status: Application granted

Method and system for estimating state variables of a moving object with modular sensor fusion

A computer-implemented method is provided for estimating state variables of a moving object, which includes: propagating core state variables of the moving object utilizing a recursive Bayesian filter and observation values from sensors from start-up of the moving object; forming, utilizing observation values from one or more additional sensors added after start-up, a covariance matrix of the recursive Bayesian filter; updating the covariance matrix based on observation values formed by at least one additional sensor; and, ascertaining the covariance of the core state variables of the additional sensor at a time after start-up.

  • Date: November 15, 2021
  • Authors: Christian Brommer, Stephan Weiss
  • Patent Number: A 50969/2020
  • Status: published