Flight Calibration Research Articles

Challenges for In-Flight Calibration of Thermal Infrared Instruments for Earth Observation

Satellite instruments operating in the thermal infrared wavelength range >3 µm provide information for applications such as land surface temperature (LST), sea surface temperatures (SST), land surface emissivity, land classification, soil composition, volcanology, fire radiative power, cloud masking, aerosols, and trace gases. All these instruments are dependent on blackbody (BB) calibration sources to provide the traceability of the radiometric calibration to SI (Système International d’Unités). A key issue for flight BB sources is to maintain the traceability of the radiometric calibration from ground to orbit. For example, the temperature of the BB is measured by a number of precision thermometers that are calibrated against a reference Standard Platinum Resistance Thermometer (SPRT) to provide the traceability to the International Temperature Scale of 1990 (ITS-90). However, once calibrated the thermometer system is subject to drifts caused by on-ground testing, the launch and space environments. At best the uncertainties due to thermometer ageing can only be estimated as there is no direct method for recalibrating. Comparisons with other satellite sensors are useful for placing an upper limit on calibration drifts but do not themselves provide a traceable link to the SI. In this paper, we describe we describe some of the technology developments, including phase change cells for use as reference standards, thermometer readout electronics and implementation of novel coatings, that are in progress to enhance the traceability of flight calibration systems in the thermal infrared.

PENGARUH KOMPETENSI PEGAWAI DAN MOTIVASI KERJA TERHADAP PRODUKTIVITAS KERJA DI BALAI KALIBRASI FASILITAS PENERBANGAN

As an organization tasked with carrying out aviation calibration aviation activities, the Aviation Facility Calibration Center must be able to provide calibration services to all airports in Indonesia with high quality and on time as scheduled. To carry out these tasks, the Aviation Facility Calibration Center urgently needs the support of quality resources. To prove this effort, this research was carried out as a study to review the productivity of flight calibration staff. The object of this study is the staff ofthe Flight Calibration Facility Center Ministry of Transportation. According to the Slovin Formula, taking sample was done by the procedure of proportionate stratified random sampling. The sample was taken by fifty participants. The findings show that productivity is very dependent on competence. while motivation becomes the dominant condition variable for work attitudes and behavior.
 Keywords: Competence, Motivation, Productivity

Flight tests of the computational reconfigurable imaging spectrometer

We present the first flight data using a Computational Reconfigurable Imaging Spectrometer (CRISP) system. CRISP (Sullenberger et al., 2017) is a novel hyperspectral thermal imaging spectrometer that uses computational imaging to enable high sensitivity measurements (via spectral multiplexing) from smaller, noisier, and less-expensive components (e.g., uncooled microbolometers) making it useful on small space and air platforms with strict size, weight, and power requirements. In contrast to other multiplexing hyperspectral solutions (e.g Michelson interferometer), it does not require moving parts, allowing for a robust system without aggressive engineering solutions. We discuss flight system design and calibration. Spectra from ground targets and gaseous species are compared to performance expectations. We successfully demonstrate the ability to extract airborne longwave infrared (8–12 μm) imagery and spectra from an uncooled camera-based CRISP system.

The TUS Space Photodetector Relative Calibration in Flight

The TUS experiment is aimed to study the energy spectrum and arrival direction of Ultra High Energy Cosmic Rays at E ∼ 100 EeV from the space orbit by measuring the fluorescence radiation of the Extensive Atmospheric Shower in the atmosphere. It is the first orbital telescope aimed for such measurements and is taking data since April 28, 2016. During the first turns of operation ∼20% PMTs were broken due to the HV tuning system failure. For the same reason, the properties of the remaining PMTs are changed. Relative calibration of PMT gains in flight was done and presented based on analyzing TUS background data itself. A reconstruction of EAS arrival directions is done using the relative calibration coefficients.

Estimation of Wind Conditions Utilizing RC Helicopter Dynamics

This paper investigates the applicability of a remote-controlled (RC) helicopter as a sensing platform for measuring local wind conditions. A simplified nonlinear multibody helicopter dynamics model has been proposed in this paper, which models local wind conditions in addition to capturing essential helicopter states such as fuselage dynamics, rotor inflow, blade flapping, and lead lagging. The critical aerodynamic parameters for the model were extracted using indoor calibration flights. This paper also presents the performance of particle swarm optimization in optimizing and validating the helicopter's dynamic model parameters. An in-house developed multisensor instrumentation system was used to track the helicopter dynamics and extract wind model parameters through anomalies in the helicopter dynamics estimates. A three-dimensional (3-D) map of local wind conditions was generated for a controlled turbulent wind environment created in an indoor test facility. To validate the system's performance, wind parameters estimated from the proposed system were quantitatively compared against the experimentally generated 3-D wind map.

Numerical Calibration of a Low-Speed sUAS Flush Air Data System

AbstractA method using computational fluid dynamics to numerically calibrate a flush air data system is presented. A small unmanned aircraft system (sUAS) has been equipped with a flush air data system and experimentally tested. The flush air data system uses computational fluid dynamics to train neural networks and is validated using the in-flight data that were previously collected. Results of the flight validation are presented, along with ways to improve the accuracy of the system. Several different calibration approaches are presented and compared with each other. The best-case results with the in-flight calibration are 0.59° and 0.66° for angle of attack and sideslip, respectively, whereas the best-case results when calibrated with computational fluid dynamics data are 0.78° and 0.90°. It is also possible to estimate other air data parameters, such as dynamic pressure, static pressure, and density, with neural networks, but the direct calculation is more accurate. Calibrating the system numerically, such as with the use of computational fluid dynamics, removes the need for any calibration flights. Although not as accurate as the in-flight calibration, numerical calibration is possible and can save the user time and expense.

Проблемы калибровки измерительных средств российских спутников дистанционного зондирования Земли

The article deals with modern photogrammetric production’s problems appearing at processing the Russian Earth remote sensing data. It is found out that todaythe main of them consists in the absence till now of the working system fortransferring linear and angular measures from national standard to the workingmeasuring devices. The necessity of creating a three-staged calibration scheme, which would guarantee the highest accuracy and stability of operating on-board measuring equipment, is justified. In addition, it is noted, that the existing technology of Earth remote sensing data processing does notprovide correct using of calibrated metrological parameters of the measuring equipment. The suggestions for eliminating that imperfection are given. The essence of the flight calibration principle foron-board equipment is formulated. The necessary list of the surveying systems’ metrological parameters and target equipment is defined.

Design and Implementation of Flight Monitoring Simulation Training System

The calibration flight is an important technical means to verify the performance and accuracy of the TT&C equipment. In the flying, the equipment is power-on/power-off and the transponder mode is switched according to the needs. The transponder is a borrower. In the case of giving-back, it is especially important to recurring maintenance for the attachment. Through the system design, the original monitoring standby machine, the analog power supply chassis and the analogue controllers state of the transponder state, and three Bosch card and one serial server are used to fully simulate the on-board application environment. The industrial tablet application software adopts C# design to realize effective information interaction with the monitoring standby machine through serial port and network communication. The characteristics of the system are the continuous assessment of the power-on maintenance of spare parts, personnel training and actual system software, which is of great significance to the actual work.

EVALUATION AND CALIBRATION OF FIXED-WING MULTISENSOR UAV MOBILE MAPPING SYSTEM: IMPROVED RESULTS

Abstract. Unmanned Aerial Vehicles (UAVs) are willingly used in photogrammetry and remote sensing, especially for image acquisition, and are characterised by high spatial resolution. UAVs can be used for the fast and, if necessary, frequent acquisition of spatial data, especially for small areas. In recent years, new trends in the development of UAVs have emerged, including the integration of various sensors and the application of ultralight laser scanners. Within the described experiment, UAV data, i.e. RGB and NIR imagery, as well as ALS data were obtained over three test areas. For one test area, the flight calibration was performed. 3 strips were oriented perpendicularly to another 3 strips and the flight was performed on two different heights: 120 and 150 m. In order to process the data acquired for the next 3 test areas, the determined calibration parameters were utilised. The oriented images were used to generate RGB and NIR ortophotos, as well as the point cloud using the Dense Image Matching (DIM) algorithm. Height differences between UAV Laser Scanning (ULS) and DIM clouds were calculated for all test areas. Experiment data from Terrestrial Laser Scanning and check points measured with GPS RTK have been used. Finally, an accuracy of less than 10 cm was achieved for the DTM. The results were improved by eliminating the problem of horizontal accuracy, but its influence is still slightly visible on the vertical accuracy of the data. The experiment proved the quality of data obtained with the ultralight scanner mounted on the platform moving with much more speed, being an alternative to manned flight missions and multi-rotors UAVs.

Analysis on Systematic Errors of Aeromagnetic Compensation Caused by Measurement Uncertainties of Three-Axis Magnetometers

Aeromagnetic surveys are important in geophysical prospecting and magnetic anomaly detection. Magnetic fields are typically measured by optically pumped magnetometers (OPMs) mounted on an aircraft. Platform-generated magnetic interference severely compromises the sensitivity of the OPMs. Therefore, aeromagnetic compensation is necessary. However, measurement uncertainties of three-axis magnetometers influence the qualities of aeromagnetic compensation and there is no method that can directly predict the qualities of aeromagnetic compensation before calibration flights. To address this issue, we propose a method to calculate the systematic errors of aeromagnetic compensation caused by measurement uncertainties of three-axis magnetometers and analyze the performance of aeromagnetic compensation in advance of calibration flights. It can be used to estimate the residual errors of aeromagnetic compensation theoretically. Using this method, researchers can assess whether aircraft platforms are appropriate to implement aeromagnetic surveys or not before carrying out experiments in practice. Field experiments are carried out to exhibit how to use the method to calculate the measurement uncertainties of aeromagnetic compensation in different conditions. The results of the experiments demonstrate the validity of the method.

Test and Simulation of 9960Hz Subcarrier Modulation for DVOR Station of Civil Aviation

In order to solve the problem of 9960Hz subcarrier modulation of DVOR system exceeding the limit, this paper use the test system and three-dimensional modelling and simulation technology to ensure flight calibration passes smoothly. Taking an airport for example, the field test and modeling simulation are carried out in the same situation when the surrounding site and parameters are the same with the flight calibration, ensuring that the results are in good agreement with the flight calibration results. We can get that the substation is the key factor which affects the 9960Hz subcarrier modulation exceeding the limit. After removing the substation, 9960Hz subcarrier modulation meet the requirements, the airport pass the flight calibration one-time finally. This method solves the problem of the 9960Hz subcarrier modulation in a DVOR station and provides the reference basis for the problems encountered in the construction and operation of the navigation station, which ensuring the safety and efficiency of air transportation.

Correction and compensation of an airborne fluxgate magnetic tensor gradiometer

An airborne fluxgate magnetic tensor gradiometer is built on fluxgates to measure directional derivatives of the magnetic field. It has been used to carry out many geophysical exploration programs quickly and efficiently. However, two key issues greatly reduce the data quality of a tensor gradiometer. One is that the fluxgate magnetic tensor gradiometer suffers various errors, such as scale drift, non-orthogonality, misalignment, zero offset, dynamic, and nonlinear errors of individual fluxgates, along with differences between characteristics of fluxgates. The other is that manoeuvring an aircraft flying in the geomagnetic field can generate magnetic interference effects on a tensor gradiometer. Regarding the common airborne fluxgate magnetic tensor gradiometer that has a cross-shaped structure, we have proposed the magnetic interference model of the aircraft and the error model of a single fluxgate. Then we have seamlessly combined these two models into the unified calibration model of a tensor gradiometer by a recursive method. Finally, we have simultaneously determined the correction coefficients and the magnetic properties of the aircraft by a calibration flight at high altitude in an area of low magnetic gradient. We have evaluated the performance of the proposed method through simulation and actual flight results using a microlight aircraft. The root-mean-square noise of each component has reached the level of less than 1.5 nT/m, and the improvement ratios are from 4096 to 17444 in terms of the measured field data of tensor components. The proposed method reduces the reliance of the installation on the aircraft and can easily be applied to other tensor gradiometers, such as airborne superconducting magnetic tensor gradiometers.

INTEGRATED MICROMECHANICAL GYROVERTICAL

The dubiousness of instantiation of the gyroverticales which based on micromechanical accelerometers and on micromechanical gyroscopic sensors is shown. Based on the analysis of the frequency characteristics of the errors of micromechanical gyroscopes and accelerometers, the expediency of their integration using the method of mutual compensation is shown. The algorithms and results of research of the integrated micromechanical gyroverticales which are based on compensation schemes with first-order and third-order dynamic filters with forcing are given. The approaches to the solution of the problem of the calibration integrated micromechanical gyroverticales in the flight are shown. The conducted researches of the proposed gyrovertical with the flight's calibration and with correction scheme showed good filtering properties and acceptable accuracy of measuring angular orientation parameters.

Time-of-flight PET time calibration using data consistency

This paper presents new data driven methods for the time of flight (TOF) calibration of positron emission tomography (PET) scanners. These methods are derived from the consistency condition for TOF PET, they can be applied to data measured with an arbitrary tracer distribution and are numerically efficient because they do not require a preliminary image reconstruction from the non-TOF data. Two-dimensional simulations are presented for one of the methods, which only involves the two first moments of the data with respect to the TOF variable. The numerical results show that this method estimates the detector timing offsets with errors that are larger than those obtained via an initial non-TOF reconstruction, but remain smaller than of the TOF resolution and thereby have a limited impact on the quantitative accuracy of the activity image estimated with standard maximum likelihood reconstruction algorithms.

A ground-based test facility for airborne magnetic gradient tensor instruments simulating calibration flights

Progress is slow in terms of the research and evaluation of calibration algorithms for full tensor magnetic gradient instruments using airborne tests. The main reason is that, based on knowledge gained by actual calibration flights, problems exist regarding high risk, high costs, and long development cycles. In this paper, we describe a ground-based simulation facility for calibration flights which combines the nonlinear aerodynamic model with a magnetic interference model. Environmental magnetic fields can be calculated and produced by tri-axial coils, which are measured by the magnetic tensor gradiometer in calibration flights. Influence from systematic errors and magnetic interference can be extracted from the simulated calibration flight provided by the facility. Compared to system evaluation in airborne operation, this method has the benefit of zero risk, low costs, and short duration of evaluation cycles. In view of ground-based multi-degree of freedom motion platforms, it has the advantages of simple manufacture, good dynamic characteristics, and adaptability to different aircraft types.

Basic Geometric Support of Systems for Earth Observation from Geostationary and Highly Elliptical Orbits

A set of standardized models and algorithms for geometric normalization and georeferencing images from geostationary and highly elliptical Earth observation systems is considered. The algorithms can process information from modern scanning multispectral sensors with two-coordinate scanning and represent normalized images in optimal projection. Problems of the high-precision ground calibration of the imaging equipment using reference objects, as well as issues of the flight calibration and refinement of geometric models using the absolute and relative reference points, are considered. Practical testing of the models, algorithms, and technologies is performed in the calibration of sensors for spacecrafts of the Electro-L series and during the simulation of the Arktika prospective system.

Fluorescence Imaging Spectrometer (FLORIS) for ESA FLEX Mission

The Fluorescence Explorer (FLEX) mission has been selected as ESA’s 8th Earth Explorer mission. The primary objectives of the mission are to provide global estimates of vegetation fluorescence, actual photosynthetic activity, and vegetation stress. FLEX will fly in tandem formation with Sentinel-3 providing ancillary data for atmospheric characterization and correction, vegetation related spectral indices, and land surface temperature. The purpose of this manuscript is to present its scientific payload, FLORIS, which is a push-broom hyperspectral imager, flying on a medium size platform. FLORIS will measure the vegetation fluorescence in the spectral range between 500 nm and 780 nm at medium spatial resolution (300 m) and over a swath of 150 km. It accommodates an imaging spectrometer with a very high spectral resolution (0.3 nm), to measure the fluorescence spectrum within two oxygen absorption bands (O2A and O2B), and a second spectrometer with lower spectral resolution to derive additional atmospheric and vegetation parameters. A compact opto-mechanical solution is the current instrument baseline. A polarization scrambler is placed in front of a common dioptric telescope serving both spectrometers to minimize the polarization sensitivity. The telescope images the ground scene onto a double slit assembly. The radiation is spectrally dispersed onto the focal planes of the grating spectrometers. Special attention has been given to the mitigation of stray-light which is a key factor to reach good accuracy of the fluorescence measurement. The absolute radiometric calibration is achieved by observing a dedicated Sun illuminated Lambertian diffuser, while the spectral calibration in flight is performed by means of vicarious techniques. The thermal stabilization is achieved by using two passive radiators looking directly to the cold space, counterbalanced by heaters in a closed loop system. The focal planes are based on custom developed CCDs. The opto-mechanical design is robust, stable vs. temperature and easy to align. The optical quality is very good as recently demonstrated by the latest tests of an elegant breadboard. The scientific data products comprise the Top Of Atmosphere (TOA) radiance measurements as well as fluorescence estimates and higher-level products related to the health status of the vegetation addressing a wide range of applications from agriculture to forestry and climate.

An autonomous lab on a chip for space flight calibration of gravity-induced transcellular calcium polarization in single-cell fern spores.

This report describes the development of lab-on-a-chip device designed to measure changes in cellular ion gradients that are induced by changes in gravitational (g) forces. The bioCD presented here detects differential calcium ion concentrations outside of individual cells. The device includes sufficient replicates for statistical analysis of the gradients around multiple single cells and around control wells that are empty or include dead cells. In the data presented, the degree of the cellular response correlates with the magnitude of the g-force applied via rotation of the bioCD. The experiments recorded the longest continuous observation of a cellular response to hypergravity made to date, and they demonstrate the potential utility of this device for assaying the threshold of cells' g-force responses in spaceflight conditions.

CALIBRATION PROCEDURES ON OBLIQUE CAMERA SETUPS

Beside the creation of virtual animated 3D City models, analysis for homeland security and city planning, the accurately determination of geometric features out of oblique imagery is an important task today. Due to the huge number of single images the reduction of control points force to make use of direct referencing devices. This causes a precise camera-calibration and additional adjustment procedures. <br><br> This paper aims to show the workflow of the various calibration steps and will present examples of the calibration flight with the final 3D City model. In difference to most other software, the oblique cameras are used not as co-registered sensors in relation to the nadir one, all camera images enter the AT process as single pre-oriented data. This enables a better post calibration in order to detect variations in the single camera calibration and other mechanical effects. <br><br> The shown sensor (Oblique Imager) is based o 5 Phase One cameras were the nadir one has 80 MPIX equipped with a 50 mm lens while the oblique ones capture images with 50 MPix using 80 mm lenses. The cameras are mounted robust inside a housing to protect this against physical and thermal deformations. The sensor head hosts also an IMU which is connected to a POS AV GNSS Receiver. The sensor is stabilized by a gyro-mount which creates floating Antenna –IMU lever arms. They had to be registered together with the Raw GNSS-IMU Data. <br><br> The camera calibration procedure was performed based on a special calibration flight with 351 shoots of all 5 cameras and registered the GPS/IMU data. This specific mission was designed in two different altitudes with additional cross lines on each flying heights. The five images from each exposure positions have no overlaps but in the block there are many overlaps resulting in up to 200 measurements per points. On each photo there were in average 110 well distributed measured points which is a satisfying number for the camera calibration. In a first step with the help of the nadir camera and the GPS/IMU data, an initial orientation correction and radial correction were calculated. With this approach, the whole project was calculated and calibrated in one step. During the iteration process the radial and tangential parameters were switched on individually for the camera heads and after that the camera constants and principal point positions were checked and finally calibrated. <br><br> Besides that, the bore side calibration can be performed either on basis of the nadir camera and their offsets, or independently for each camera without correlation to the others. This must be performed in a complete mission anyway to get stability between the single camera heads. Determining the lever arms of the nodal-points to the IMU centre needs more caution than for a single camera especially due to the strong tilt angle. <br><br> Prepared all these previous steps, you get a highly accurate sensor that enables a fully automated data extraction with a rapid update of you existing data. Frequently monitoring urban dynamics is then possible in fully 3D environment.

CALIBRATION PROCEDURES ON OBLIQUE CAMERA SETUPS

Abstract. Beside the creation of virtual animated 3D City models, analysis for homeland security and city planning, the accurately determination of geometric features out of oblique imagery is an important task today. Due to the huge number of single images the reduction of control points force to make use of direct referencing devices. This causes a precise camera-calibration and additional adjustment procedures. This paper aims to show the workflow of the various calibration steps and will present examples of the calibration flight with the final 3D City model. In difference to most other software, the oblique cameras are used not as co-registered sensors in relation to the nadir one, all camera images enter the AT process as single pre-oriented data. This enables a better post calibration in order to detect variations in the single camera calibration and other mechanical effects. The shown sensor (Oblique Imager) is based o 5 Phase One cameras were the nadir one has 80 MPIX equipped with a 50 mm lens while the oblique ones capture images with 50 MPix using 80 mm lenses. The cameras are mounted robust inside a housing to protect this against physical and thermal deformations. The sensor head hosts also an IMU which is connected to a POS AV GNSS Receiver. The sensor is stabilized by a gyro-mount which creates floating Antenna –IMU lever arms. They had to be registered together with the Raw GNSS-IMU Data. The camera calibration procedure was performed based on a special calibration flight with 351 shoots of all 5 cameras and registered the GPS/IMU data. This specific mission was designed in two different altitudes with additional cross lines on each flying heights. The five images from each exposure positions have no overlaps but in the block there are many overlaps resulting in up to 200 measurements per points. On each photo there were in average 110 well distributed measured points which is a satisfying number for the camera calibration. In a first step with the help of the nadir camera and the GPS/IMU data, an initial orientation correction and radial correction were calculated. With this approach, the whole project was calculated and calibrated in one step. During the iteration process the radial and tangential parameters were switched on individually for the camera heads and after that the camera constants and principal point positions were checked and finally calibrated. Besides that, the bore side calibration can be performed either on basis of the nadir camera and their offsets, or independently for each camera without correlation to the others. This must be performed in a complete mission anyway to get stability between the single camera heads. Determining the lever arms of the nodal-points to the IMU centre needs more caution than for a single camera especially due to the strong tilt angle. Prepared all these previous steps, you get a highly accurate sensor that enables a fully automated data extraction with a rapid update of you existing data. Frequently monitoring urban dynamics is then possible in fully 3D environment.