In-field Calibration Research Articles

Calibration and field evaluation of the Chemcatcher® passive sampler for monitoring metaldehyde in surface water

Metaldehyde is a potent molluscicide. It is the active ingredient in most slug pellets used for crop protection. This polar compound is considered an emerging pollutant. Due to its environmental mobility, metaldehyde is frequently detected at impacted riverine sites, often at concentrations above the EU Drinking Water Directive limit of 0.1µgL−1 for an individual pesticide. This presents a problem when such waters are abstracted for use in the production of potable water supplies, as this chemical is difficult to remove using conventional treatment processes. Understanding the sources, transport and fate of this pollutant in river catchments is therefore important. We developed a new variant of the Chemcatcher® passive sampler for monitoring metaldehyde comprising a Horizon Atlantic™ HLB-L disk as the receiving phase overlaid with a polyethersulphone membrane. The sampler uptake rate (Rs) was measured in semi-static laboratory (Rs = 15.7mLday−1) and in-field (Rs = 17.8mLday−1) calibration experiments. Uptake of metaldehyde was linear over a two-week period, with no measurable lag phase. Field trials (five consecutive 14day periods) using the Chemcatcher® were undertaken in eastern England at three riverine sites (4th September-12th November 2015) known to be impacted by the seasonal agricultural use of metaldehyde. Spot samples of water were collected regularly during the deployments, with concentrations of metaldehyde varying widely (~ 0.03–2.90µgL−1) and often exceeding the regulatory limit. Time weighted average concentrations obtained using the Chemcatcher® increased over the duration of the trial corresponding to increasing stochastic inputs of metaldehyde into the catchment. Monitoring data obtained from these devices gives complementary information to that obtained by the use of infrequent spot sampling procedures. This information can be used to develop risk assessments and catchment management plans and to assess the effectiveness of any mitigation and remediation strategies.

An Algorithm for the In-Field Calibration of a MEMS IMU

Recently, micro electro-mechanical systems (MEMS) inertial sensors have found their way in various applications. These sensors are fairly low cost and easily available but their measurements are noisy and imprecise, which poses the necessity of calibration. In this paper, we present an approach to calibrate an inertial measurement unit (IMU) comprised of a low-cost tri-axial MEMS accelerometer and a gyroscope. As opposed to existing methods, our method is truly infield as it requires no external equipment and utilizes gravity signal as a stable reference. It only requires the sensor to be placed in approximate orientations, along with the application of simple rotations. This also offers easier and quicker calibration comparatively. We analyzed the method by performing experiments on two different IMUs: an in-house built IMU and a commercially calibrated IMU. We also calibrated the in-house built IMU using an aviation grade rate table for comparison. The results validate the calibration method as a useful low-cost IMU calibration scheme.

Built-in-Self-Calibration for I/Q Imbalance in Wideband Millimeter-Wave Gigabit Transmitters

This paper addresses the estimation and compensation of I/Q imbalance, one of the most prominent impairments found in wideband zero-intermediate frequency transceivers (TRxs). The I/Q imbalance encountered in this kind of TRx comprises not only frequency-selective gain and phase imbalance but also delay imbalance. Unless appropriate compensation is applied, the I/Q imbalance significantly degrades the performance of a communication system. This paper presents a novel compensation technique for transmitter I/Q imbalance based on built-in-self-calibration, a low cost and robust compensation technique that enables manufacturing as well as in-field calibration with low computational complexity. The method’s performance is evaluated in a TRx with 64-quadratic-amplitude modulation and 2 GHz of bandwidth implemented with real hardware. The measurements show that the proposed technique achieves an image rejection ratio greater than 35 dB in the entire 2 GHz bandwidth and an error vector magnitude lower than 3%.

In-Flight Calibration of Gyros and Star Sensor With Observability Analysis for SINS/CNS Integration

The in-flight or in-field calibration of gyro in terms of all-parameter errors and star sensor installation errors is vital for improving the hitting accuracy and quick reaction capability of the SINS/CNS Integration system for near-earth flight vehicles. This paper explores an in-flight or in-field decoupled four-position calibration method by analyzing the degree of observability of error states based on singular values. Using this approach, an effort is made to isolate individual error sources to prevent contamination by using the least number of tests. The observability matrix is decoupled into three categories of submatrix: the gyro-bias observability matrix, gyro-scale factor observability matrix, and the gyro-misalignments and star sensor installation error observability matrix. In this paper, it is suggested that the observability degree of gyro-bias is proportional to the integration time, while the other gyro errors and the star sensor installation errors are proportional to the angular increments. Covariance analysis with a Kalman filter is performed, which confirm these conclusions. Theoretical simulations showed a reduction in the gyro all-parameter errors and the star sensor installation errors variance and in the time required to achieve convergence with the angular increments of the three-axis direction in a few minutes.

Mission Planning for the Estimation of the Field Coverage of Unmanned Aerial Systems in Monitoring Mission in Precision Farming

In the recent years, Unmanned Aerial Systems (UAS) have been largely employed in civil applications, such as aerial photography and topographic mapping, environmental monitoring, search and rescue, prevent of fires and disasters, environmental research and general photography and videos. Nevertheless, according to (AUVSI, 2013), agriculture is the main application where UAS will be employed in the near future. Small Unmanned Aerial Vehicles (UAVs) are flexible, easy to use and relative low-cost; thus, they can be employed in monitoring activities in precision farming, ensuring a prompt reaction to plant disease, lack of plants nutrients and environmental changes that are the main focus for farm efficiency and productivity. Recent development in high-resolution remote sensing and image processing technology has yield to small- size sensors compatible with small UAV payload weight. Each kind of sensor needs a certain flight pattern over the fields. However, a Remotely Piloted Aircraft Systems (RPAS) used for specialized operations or experimental activities has to be compliant with National Civil Aviation Authority regulations. On 2015, the Italian Aviation Authority (ENAC) published the second edition of the regulatory issue for this kind of aircrafts. The aim of this paper is the management analysis of RPAS for their use in survey missions for precision faming, taking into account the Italian regulatory prescription and two different kind of commercial sensors. UAVs are considered similarly to any other farm machine, describing the operative workflow and analysing the elementary time procedures associated to the different ways of planning a flight mission of the UAS on the field to be monitored. Actual rates of works, Effective Field Capacity (EFC) and Field Efficiency (FE), field coverage and survey cost are finally provided. The analysis includes also in-field pre-flight calibration procedures.

SIMULATION OF INERTIAL NAVIGATION SYSTEM ERRORS AT AERIAL PHOTOGRAPHY FROM UAV

Abstract. The problem of accuracy determination of the UAV position using INS at aerial photography can be resolved in two different ways: modelling of measurement errors or in-field calibration for INS. The paper presents the results of INS errors research by mathematical modelling. In paper were considered the following steps: developing of INS computer model; carrying out INS simulation; using reference data without errors, estimation of errors and their influence on maps creation accuracy by UAV data. It must be remembered that the values of orientation angles and the coordinates of the projection centre may change abruptly due to the influence of the atmosphere (different air density, wind, etc.). Therefore, the mathematical model of the INS was constructed taking into account the use of different models of wind gusts. For simulation were used typical characteristics of micro electromechanical (MEMS) INS and parameters of standard atmosphere. According to the simulation established domination of INS systematic errors that accumulate during the execution of photographing and require compensation mechanism, especially for orientation angles. MEMS INS have a high level of noise at the system input. Thanks to the developed model, we are able to investigate separately the impact of noise in the absence of systematic errors. According to the research was found that on the interval of observations in 5 seconds the impact of random and systematic component is almost the same. The developed model of INS errors studies was implemented in Matlab software environment and without problems can be improved and enhanced with new blocks.

Photogrammetry using in-field calibration: a non-invasive tool for predicting sex and life stages tested on Hector's dolphins in the wild

ABSTRACTAccurate data on sex and life stage are essential for building realistic population models, which in turn are essential for sustainable conservation management. This case study develops and validates an improved photogrammetry method that allows for in-field calibration. The method was used to measure Hector's dolphins’ dorsal fins in the wild. Seven independent measurements of one dolphin resulted in a coefficient of variation of 1.39% for fin base length and 2.33% for fin height. Test measurements on shore at different distances and angles resulted in a mean error smaller than 1% up to a distance of 10 m and an angle of 40°. Dorsal fin dimensions from necropsied Hector's dolphins were analysed to evaluate the potential of predicting sex and life stage based on a dorsal fin measured in the wild. Dorsal fin shape was significantly related to sex. However, sex estimations based on this model turned out to be not accurate enough to replace traditional sexing methods for Hector's dolphins. Fin base length was significantly related to life stage for females. Estimations based on this model appear to be accurate.

Continuous and long-term measurements of reflectance and sun-induced chlorophyll fluorescence by using novel automated field spectroscopy systems

In this paper we present novel automated field spectroscopy systems for collecting unattended, continuous and long-term measurements of plant canopies and, more in general, of Earth's ecosystems. These systems simultaneously collect high and ultra-high resolution spectra in the visible to near-infrared (VNIR) domain employing two spectrometers: i) the first covers the spectral range 400–1000nm with a 1.0nm spectral resolution; ii) the second provides a sub-nanometer spectral resolution within the 700–800nm spectral range. The data collected by the first spectrometer allow retrieval of VNIR reflectance, while the higher spectral resolution data from the second device permit estimation of vegetation Sun-Induced Fluorescence (SIF) in the O2–A band. The instruments are constructed by assembling commercial and on-the-shelf optoelectronic devices to facilitate reproduction of the instrument for promoting measurements over different ecosystems. The instrument's optical design, data collection and processing, laboratory and in-field calibration methods are reported and discussed. The high spectral resolution and the rigorous calibration methods enable accurate estimation of SIF in physical units by exploiting almost the same retrieval concept as that of the European Space Agency FLuorescence EXplorer mission. The instruments have been operated in several field campaigns with the aim to show: i) the possibility of continuous and seasonal monitoring of plant growth and activity of an agricultural crop; and ii) the diverse and specific daily course patterns of different types of canopy. The datasets of canopy reflectance, vegetation indices and SIF collected are shown and discussed.

In-field fast calibration of FOG-based MWD IMU for horizontal drilling

A fiber optic gyroscope (FOG)-based measuring-while-drilling (MWD) device for horizontal drilling is developed and an in-field fast calibration method of the MWD inertial measurement unit (IMU) is presented. The IMU consists of a FOG triad and a quartz accelerometer triad. An error model for the inertial sensors is established and 12 errors are confirmed as the main error sources for horizontal drilling after an analysis. A five-rotation-in-level-plane (5RILP) in-field fast calibration scheme for the main errors of the MWD IMU is illustrated. The scheme can be conveniently implemented on an almost level plane, such as a table plane, without any special external equipment. To solve the calibrated errors, a systematic approach based on specific force measurement observation is adopted. Observation equations of the IMU errors are derived according to the rotation sequence of the calibration scheme. Simulation results show that the proposed calibration method is effective even if there are 5° errors in level and 10° errors in heading. Calibration experiments using the developed FOG-based MWD equipment on a table plane confirm the validity of the proposed in-field calibration method. Inertial navigation tests show that the actual accuracy of the MWD IMU is greatly improved by 60.6% after in-field calibration.

A field-portable membrane introduction mass spectrometer for real-time quantitation and spatial mapping of atmospheric and aqueous contaminants.

Environmental concentrations of volatile and semivolatile organic compounds (VOC/SVOCs) can vary dramatically in time and space under the influence of environmental conditions. In an industrial setting, multiple point and diffuse sources can contribute to fugitive emissions. Assessments and monitoring programs using periodic grab sampling provide limited information, often with delay times of days or weeks. We report the development and use of a novel, portable membrane introduction mass spectrometry (MIMS) system capable of resolving and quantifying VOC and SVOCs with high spatial and temporal resolution, in the field, in real-time. An electron impact ionization cylindrical ion trap mass spectrometer modified with a capillary hollow fiber polydimethylsiloxane membrane interface was used for continuous air and water sampling. Tandem mass spectrometry and selected ion monitoring scans performed in series allowed for the quantitation of target analytes, and full scan mode was used to survey for unexpected analytes. Predeployment and in-field external calibrations were combined with a continuously infused internal standard to enable real-time quantitation and monitor instrument performance. The system was operated in a moving vehicle with internet-linked data processing and storage. Software development to integrate MIMS and relevant meta-data for visualization and geospatial presentation in Google Earth is presented. Continuous quantitation enables the capture of transient events that may be missed or under-represented by traditional grab sampling strategies. Real-time geospatial maps of chemical concentration enable adaptive sampling and in-field decision support. Sample datasets presented in this work were collected in Northern Alberta in 2010-2012.

Measurement of cyclic volatile methylsiloxanes in the aquatic environment using low-density polyethylene passive sampling devices using an in-field calibration study – Challenges and guidance

Cyclic volatile methylsiloxanes (cVMS) are used in personal care products and are hydrophobic, volatile and persistent. Their environmental water concentrations are low and are difficult to detect using conventional sampling methods. This study shows the potential of passive sampling for cVMS. We used low-density polyethylene (LDPE) samplers and in-field calibration methods for octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5). 13C-D4 and 13C-D5, methyltris(trimethylsiloxy)silane (MT), tetrakis(trimethylsiloxy)silane (TK), and five deuterated polycyclic aromatic hydrocarbons (PAHs) were used as performance reference compounds (PRCs). Samplers were calibrated (7-d) using effluent at a treatment plant, with uptake of cVMS and losses of the PRCs measured at 12 time-points. Concentrations of D4 (53ngL−1) and D5 (1838ngL−1) were stable in the effluent. Uptake of D4 and loss of 13C-D4 were isotropic and equilibrium was approached by 7-d. Two estimates of sampler uptake rate (Rs) were 2.1Ld−1 and 2.5Ld−1. The estimated log LDPE/water partition coefficient was 4.4. The uptake of D5 was slower (Rs=0.32Ld−1) and equilibrium was not reached. Offloading of 13C-D5, MT and TK were slow, and isotropic behaviour was not demonstrated for D5. Offloading of PAHs followed the predicted pattern for LDPE. Uptake of cVMS appeared to be under membrane control, due to low diffusion coefficients in LDPE. Samplers can monitor time-weighted average concentrations of D4 for less than a week, and D5 for longer periods. LDPE samplers allow cVMS to be determined at lower concentrations than by spot sampling methods.

Vector-Aided In-Field Calibration Method for Low-End MEMS Gyros in Attitude and Heading Reference Systems

This paper presents a novel calibration method for the microelectromechanical system (MEMS) gyros. Comparing with the traditional gyro calibration method that requires high precision equipment, the calibration scheme presented in this paper is based on the principle that the time derivative of a reference vector can be expressed as the cross product of the angular velocity and the reference vector itself. The proposed method can use vector observations instead of precise external references, and it is well suited for the in-field calibration of attitude and heading reference systems (AHRS). Moreover, the proposed method computes all the parameters in the sensor error model through linear optimization. Numerical simulations are performed to evaluate the effectiveness of the proposed method, and experiment on a custom-built AHRS shows that the proposed calibration method has the same accuracy as the traditional method, which uses a rate table for a low-end MEMS gyro.

Measurements of hydrogen sulfide (H<sub>2</sub>S) using PTR-MS: calibration, humidity dependence, inter-comparison and results from field studies in an oil and gas production region

Abstract. Natural gas production is associated with emissions of several trace gases, some of them classified as air toxics. While volatile organic compounds (VOCs) have received much attention, hydrogen sulfide (H2S) can also be of concern due to the known health impacts of exposure to this hazardous air pollutant. Here, we present quantitative, fast time-response measurements of H2S using proton-transfer-reaction mass-spectrometry (PTR-MS) instruments. An ultra-light-weight PTR-MS (ULW-PTR-MS) in a mobile laboratory was operated for measurements of VOCs and H2S in a gas and oil field during the Uintah Basin Winter Ozone Study (UBWOS) 2012 campaign. Measurements of VOCs and H2S by a PTR-MS were also made at the Horse Pool ground site in the Uintah Basin during UBWOS 2013. The H2S measurement by PTR-MS is strongly humidity dependent because the proton affinity of H2S is only slightly higher than that of water. The H2S sensitivity of PTR-MS ranged between 0.6–1.4 ncps ppbv−1 during UBWOS 2013. We compare the humidity dependence determined in the laboratory with in-field calibrations and determine the H2S mixing ratios for the mobile and ground measurements. The PTR-MS measurements at Horse Pool are evaluated by comparison with simultaneous H2S measurements using a PTR time-of-flight MS (PTR-ToF-MS) and a Picarro cavity ring down spectroscopy (CRDS) instrument for H2S / CH4. On average 0.6 ± 0.3 ppbv H2S was present at Horse Pool during UBWOS 2013. The correlation between H2S and methane enhancements suggests that the source of H2S is associated with oil and gas extraction in the basin. Significant H2S mixing ratios of up to 9 ppmv downwind of storage tanks were observed during the mobile measurements. This study suggests that H2S emissions associated with oil and gas production can lead to short-term high levels close to point sources, and elevated background levels away from those sources. In addition, our work has demonstrated that PTR-MS can make reliable measurements of H2S at levels below 1 ppbv.

A novel network calibration method for inertial measurement units

To enhance the navigation precision of strapdown inertial navigation system, it is necessary to carry out a high accuracy calibration for the inertial measurement unit (IMU). In this paper, a novel network calibration method is proposed to satisfy the calibration for a number of IMUs, which is depending on multiple maneuvers of the test platform where IMUs are installed. With the specific maneuvers of the test platform, the uncalibrated parameters of gyros and accelerometers models can be excited. In order to obtain the optimal estimation of these parameters, the dual-loop filter algorithm based on Kalman filter is presented for the information fusion by tracking the velocity and position errors from the IMUs nearby. The simulation result shows that the parameters of gyros and accelerometers models can be well estimated in a short time. Comparing with the existing calibration methods, the proposed method has the following advantages: (1) it does not require special equipment such as a turntable to provide the angular rate and multi-position tests, (2) it is time efficient when compared with other time consuming methods, (3) it can calibrate a lot of IMUs simultaneously, but not one by one. Thus with the above advantages, the proposed calibration method will have a wide application prospect for the in-field calibration.

Electrochemical dissolved oxygen removal from microfluidic streams for LOC sample pretreatment.

Current water quality monitoring for heavy metal contaminants largely results in analytical snapshots at a particular time and place. Therefore, we have been interested in miniaturized and inexpensive sensors suitable for long-term, real-time monitoring of the drinking water distribution grid, industrial wastewater effluents, and even rivers and lakes. Among the biggest challenges for such sensors are the issues of in-field device calibration and sample pretreatment. Previously, we have demonstrated use of coulometric stripping analysis for calibration-free determination of copper and mercury. For more negatively reduced metals, O2 reduction interferes with stripping analysis; hence, most electroanalysis techniques rely on pretreatments to remove dissolved oxygen (DO). Current strategies for portable DO removal offer limited practicality, because of their complexity, and often cause inadvertent sample alterations. Therefore, we have designed an indirect in-line electrochemical DO removal device (EDOR), utilizing a silver cathode to reduce DO in a chamber that is fluidically isolated from the sample stream by an O2-permeable membrane. The resulting concentration gradient supports passive DO diffusion from the sample stream into the deoxygenation chamber. The DO levels in the sample stream were determined by cyclic voltammetry (CV) and amperometry at a custom thin-layer cell (TLC) detector. Results show removal of 98% of the DO in a test sample at flow rates approaching 50 μL/min and power consumption as low as 165 mW h L(-1) at steady state. Besides our specific stripping application, this device is well-suited for LOC applications where miniaturized DO removal and/or regulation are desirable.

Data Based Calibration System for Radar Used by Vehicle Activated Signs

The accurate measurement of a vehicle's velocity is an essential feature in adaptive vehicle acti- vated sign systems. Since the velocities of the vehicles are acquired from a continuous wave Dop- pler radar, the data collection becomes challenging. Data accuracy is sensitive to the calibration of the radar on the road. However, clear methodologies for in-field calibration have not been care- fully established. The signs are often installed by subjective judgment which results in measure- ment errors. This paper develops a calibration method based on mining the data collected and matching individual vehicles travelling between two radars. The data was cleaned and prepared in two ways: cleaning and reconstructing. The results showed that the proposed correction factor derived from the cleaned data corresponded well with the experimental factor done on site. In ad- dition, this proposed factor showed superior performance to the one derived from the recon- structed data.

Electrochemical and microfabrication strategies for remotely operated smart chemical sensors: Application of anodic stripping coulometry to calibration-free measurements of copper and mercury

Remote unattended sensor networks are increasingly sought after to monitor the drinking water distribution grid, industrial wastewater effluents, and even rivers and lakes. One of the biggest challenges for application of such sensors is the issue of in-field device calibration. With this challenge in mind, we report here the use of anodic stripping coulometry (ASC) as the basis of a calibration-free micro-fabricated electrochemical sensor (CF-MES) for heavy metal determinations. The sensor platform consisted of a photo-lithographically patterned gold working electrode on SiO2 substrate, which was housed within a custom stopped-flow thin-layer cell, with a total volume of 2–4μL. The behavior of this platform was characterized by fluorescent particle microscopy and electrochemical studies utilizing Fe(CN)63−/4− as a model analyte. The average charge obtained for oxidation of 500μM ferrocyanide after 60s over a 10 month period was 176μC, corresponding to a volume of 3.65μL (RSD=2.4%). The response of the platform to copper concentrations ranging from 50 to 7500ppb was evaluated, and the ASC results showed a linear dependence of charge on copper concentrations with excellent reproducibility (RSD≤2.5%) and accuracy for most concentrations (≤5–10% error). The platform was also used to determine copper and mercury mixtures, where the total metallic content was measurable with excellent reproducibility (RSD≤4%) and accuracy (≤6% error).

In-field calibration of the Navigation Dosimetry System (NAVIDOS) during solar minimum conditions

The NAVIgation DOsimetry System (NAVIDOS) comprises a complete readout system for a radiation detec- tor, an air pressure sensor and a GPS receiver. The detector system DOSTEL uses silicon detectors which make NAVI- DOS light weighted and compact in size. Therefore, NAVI- DOS is well suited to be installed on board aircraft. The cal- ibration of NAVIDOS in terms of ambient dose equivalent is done by an in-field comparison with the PTB reference in- strument DOS. We also show that the dependence of these results on the vertical cut-off rigidity can be explained by the low response of the silicon detectors for neutrons. Therefore, in-flight measurements have been performed together with the PTB reference instrument DOS. The dose rates, cal- culated using the PTB code FDOScalc, were verified with these DOS measurements. The calibration of NAVIDOS was done with FDOScalc and results in calibration factors between 3.4 in the polar and 2.4 in the equator region.

The Impact of Noise and Mismatch on SAR ADCs and a Calibratable Capacitance Array Based Approach for High Resolutions

Abstract This paper describes widely used capacitor structures for charge-redistribution (CR) successive approximation register (SAR) based analog-to-digital converters (ADCs) and analyzes their linearity limitations due to kT/C noise, mismatch and parasitics. Results of mathematical considerations and statistical simulations are presented which show that most widespread dimensioning rules are overcritical. For high-resolution CR SAR ADCs in current CMOS technologies, matching of the capacitors, influenced by local mismatch and parasitics, is a limiting factor. For high-resolution medium-speed CR SAR ADCs, a novel capacitance array based approach using in-field calibration is proposed. This architecture promises a high resolution with small unit capacitances and without expensive factory calibration as laser trimming.

One new onboard calibration scheme for gimbaled IMU

In most cases, a gimbaled inertial measurement unit (IMU) can provide more accurate navigation information than a strap-down IMU when there is no navigation aiding of global positioning system (GPS) or other equipments. The gimbaled IMU is still used in self-contained precision navigation systems such as launch vehicles, missiles and vessels.To guarantee precision navigation, it is necessary to carry out in-field calibration for the gimbaled IMU before a mission. It is not fit to adopt multi-position calibration method to calibrate the gimbaled IMU mounted on a carrier on the sea because the signal to noise ratio (SNR) of gyro and accelerometer is low when the gimbals are locked. Traditional continuous calibration methods which use measured acceleration to calibrate gyros and accelerometers are not fit either because of the lever-arm errors caused by the vessel’s attitude motion.Focusing on the problem above, this paper proposes a new calibration scheme. The gyro parameters are calibrated separately through measured gimbal angles and the accelerometer parameters are calibrated by a “shape-from-motion” method without attitude information.Keeping the gimbals unlocked and rotating the gimbals continuously, the measured gimbal angles can be used to calibrate gyro parameters and case misalignments as the IMU is mounted on a gyro-stabilized platform. Because the gyro errors and case misalignments propagate nonlinearly in gimbal angles error model, a nonlinear estimation filer, spherical simplex unscented Kalman filter (SSUKF), is adopted to deal with this problem. Besides, the parameters’ observability is analyzed by the singular value analysis of the observability matrix and the theory of relative output sensitivity and a continuous calibration scheme is established. Simulation for the proposed calibration scheme is conducted and the sensitivity to environment disturbances is analyzed. It is shown that the proposed method can calibrate onboard gimbaled IMU with high precision and proves practical in dealing with environment disturbances.