Temporal Drift Research Articles

Quantum mechanical current-to-voltage conversion with quantum Hall resistance array

Accurate measurement of the electric current requires a stable and calculable resistor for an ideal current-to-voltage conversion. However, the temporal resistance drift of a physical resistor is unavoidable, unlike the quantum Hall resistance directly linked to the Planck constant h and the elementary charge e. Lack of an invariant high-resistance leads to a challenge in making small-current measurements below 1 µA with an uncertainty better than one part in 106. In this work, we demonstrate a current-to-voltage conversion in the range from a few nano amps to one microamp with an invariant quantized Hall array resistance. The converted voltage is directly compared with the Josephson voltage reference in the framework of Ohm’s law. Markedly distinct from the classical conversion, which relies on an artifact resistance reference, this current-to-voltage conversion does not demand timely resistance calibrations. It improves the precision of current measurement down to 8 × 10−8 at 1 µA.

Repetition-rate multiplicable soliton microcomb generation and stabilization via phase-modulated pumping scheme

We numerically demonstrate repetition rate multiplicable soliton microcomb generation using the phase-modulation pump scheme (PMS). Dissipative Kerr solitons are directly obtained avoiding the primary comb and chaotic modulation-instability stage and the repetition rate can be multiplied by changing the modulation frequency with fixed intensity. The PMS can not only help to stabilize emitted solitons with inhibited temporal drift against the Raman self-frequency shift effect, but also achieve soliton spacing equalization recovered from certain position fluctuations. Such approach can enable delicate manipulation on soliton behaviors, and provide a feasible route to soliton microcombs with even higher repetition rates and improved stabilities.

Temperature and temporal drift compensation for Al2O3-gate ISFET-based pH sensor using machine learning techniques

This work presents modeling of temperature and temporal drift characteristics of Al2O3-gate Ion-Sensitive Field-Effect Transistor (ISFET) and performance enhancement of ISFET-based pH sensor by using machine learning (ML) techniques. The behavioral macromodel of ISFET is built using Simulation Program with Integrated Circuit Emphasis (SPICE), which incorporates the temperature and temporal dependent behavior of electrochemical and device parameters. The SPICE macromodel for ISFET is exported as a subcircuit block for designing the constant-voltage (CV) constant-current (CC) readout circuit. The training, validation and testing data for machine learning techniques was generated using SPICE simulations for experimental analysis. We compensate the temperature drift of the sensor by applying well-known ML techniques to its read out integrated circuit (ROIC) output. We learned the salient characteristics from the simulated data with neural networks, linear regression, support vector machines, decision trees and random forests, respectively, in order to achieve temperature drift compensated ROIC outputs for unseen data. Our results show that random forest technique achieves lowest error rates for Al2O3-gate ISFET-based pH sensor. The temperature compensated ISFET ROIC output shows excellent performance with ΔpH less than 0.025 for pH range 2–12 over a temperature range of 15 °C to 45 °C. We adopt Bayesian inference technique to capture and compensate the temporal drift in the device. The analysis shows credibility of estimated values and robustness of the Bayesian approach to temporal compensation for temperature ranging from 15 °C to 45 °C. Overall, this work provides a framework for designing robust and intelligent ISFET-based pH sensors by modeling the drift characteristics and compensating it using ML techniques.

Modeling and simulation of temporal and temperature drift for the development of an accurate ISFET SPICE macromodel

Modeling of non-idealities in ion-sensitive field-effect transistors (ISFET) is crucial for obtaining precise pH-sensing characteristics. This paper presents an accurate Simulation Program with Integrated Circuit Emphasis (SPICE) macromodel of a $$\hbox {Si}_{3}\hbox {N}_{4}$$–gate ISFET pH sensor which takes into account the temperature and temporal drift. The robust model includes surface site densities of both the silanol and primary amine sites, which were approximated in previously reported ISFET macromodels. We use a thermodynamic model to incorporate the variation of dissociation constants with temperature to achieve a better fit with experimental data reported in the literature. Several regression iterations are performed, and an average adjusted R-squared value of 0.9992 is obtained. The transfer characteristics of the device obtained from the extracted parameters are in good agreement with the experimentally reported values, with an error of 3.53% and 2.29% between the reported and modeled isothermal points for gate voltage ($${V}_{\mathrm{GS}}$$) and drain current ($${I}_{\mathrm{DS}}$$), respectively. The developed macromodel is imported in a constant voltage/constant current (CVCC) readout circuit as a subcircuit block and simulated in a temperature range of 15–$$45\, ^{\circ }\hbox {C}$$. Simulations of the CVCC readout circuit show that operating the device near the isothermal point reduces the temperature drift to approximately 0.015 pH for the pH range of human blood, i.e., pH 7.35 to 7.45. Temporal drift modeling and simulation are performed, and show a stretched exponential dependence on time, which is in good agreement with experimental results reported in the literature. Finally, we demonstrate the combined effect of temporal and temperature drift, where it is found that the temporal drift rate increases with temperature as a stretched exponential function, validating the experimentally reported values.

Upgrade of the Argentine Islands INTERMAGNET observatory at Akademik Vernadsky station, Antarctica

The article describes the main features of upgrading the magnetometric complex based on the LEMI-025 variometer in January-April 2019 at the geomagnetic observatory (code AIA) of the Ukrainian Antarctic Akademik Vernadsky station. The observatory’s old magnetometric complex consisted of two LEMI-008 (No. 02 and No. 16) variometers and one POS-1 scalar magnetometer. The measurements of LEMI-008 and POS-1 were not mutually synchronized and this was one of the main problem. Every measuring instrument taken individually as a component of the whole magnetometric complex had good individual properties. However, in general, the complex as an entire system had reduced performance, mainly due to the lack of mutual synchronization of measurements. Some preliminary test results are also presented. Main objective. One of the main task of upgrading the AIA observatory was to install a new variometer that is compatible with the requirements of the 1-second INTERMAGNET data standard. For two decades, old LEMI-008 variometers at Akademik Vernadsky station have shown high baseline stability, which meets INTERMAGNET requirements. Unfortunately, the noise characteristics of old variometers, the accuracy of synchronization with UTC, and the resolution do not longer meet the current INTERMAGNET requirements for devices that produce 1-second data. Measurements of LEMI-008 variometers and POS-1 scalar magnetometer were not mutually  synchronized. Due to lack of reliable mutual synchronization, the differences between the field vector modules, calculated indirectly from the variometer measurements and measured directly with the scalar magnetometer, varied and could be unreliable. With strong geomagnetic disturbances, this reduced the overall accuracy of the magnetometric complex as an integral measuring system, although the complex consisted of high-precision instruments. Only one of LEMI-008 variometers was equipped with GPS synchronization. This made data processing difficult. Therefore, one of the crucial upgrading tasks was creation of a system for mutual synchronization of measurements provided by the variometer LEMI-025 and the scalar magnetometer POS-1 with an accuracy of approximately 0.1 s (but not worse than 1 s) using control computer. Methods. The problem of mutual synchronization of the measurements of the LEMI-025 variometer and the POS-1 scalar magnetometer (at the stage of upgrading the magnetometric complex as a whole system) was solved using a control computer by periodical adjusting the POS-1 clock and starting its measurement cycles with a given timing advance. New data arrays were obtained while the LEMI-025 magnetometer was operated in test mode. Using the Bartlett’s method and spectral harmonics averaging, the noise level of the magnetometers during a geomagnetically quiet day was estimated. The results of absolute measurements of the geomagnetic field components, regularly carried out in the observatory by two methods, were analyzed and the baselines values of the LEMI-025 magnetometer were estimated. The comparative analysis of the records of the Earth magnetic field intensity, obtained by direct measurements with a scalar magnetometer POS-1 and calculated from the baseline-adjusted components of the LEMI-025 variometer, was performed. Using the obtained baseline values and the total field difference signals the high calibration accuracy of the new variometer was confirmed and the orientation errors of its sensitivity axes in the geographical coordinate frame were estimated. Conclusions. Our preliminary results confirm that the characteristics of new LEMI-025 variometer meet the INTERMAGNET requirements. The orientation errors of LEMI-025 sensor do not exceed 5 arc minutes. The base line is quite stable. All its components have dispersion within ±2 nT, without pronounced temporal drift. The test results of LEMI-025 variometer showed that the characteristics of all magnetometric instruments in the measuring pavilion of the AIA observatory should be mutually agreed in terms of electromagnetic compatibility.

Stability Study of an Electrothermally-Actuated MEMS Mirror with Al/SiO2 Bimorphs

Electrothermal actuation is one of the main actuation mechanisms and has been employed to make scanning microelectromechanical systems (MEMS) mirrors with large scan range, high fill factor, and low driving voltage, but there exist long-term drifting issues in electrothermal bimorph actuators whose causes are not well understood. In this paper, the stability of an bimorph electrothermal MEMS mirror operated in both static and dynamic scan mode has been studied. Particularly, the angular drifts of the MEMS mirror plate were measured over 90 h at different temperatures in the range of – °C. The experiments show that the temporal drift of the mirror plate orientation largely depends on the temperature of the electrothermal bimorph actuators. Interestingly, it is found that the angular drift changes from falling to rising as the temperature increases. An optimal operating temperature between °C to °C for the MEMS mirror is identified. At this temperature, the MEMS mirror exhibited stable scanning with an angular drift of less than °/h.

JILA SrI optical lattice clock with uncertainty of

We report on an improved systematic evaluation of the JILA SrI optical lattice clock, achieving a nearly identical uncertainty compared to the previous strontium record set by the JILA SrII optical lattice clock at . This improves upon the previous evaluation of the JILA SrI optical lattice clock in 2013, and we achieve a more than twenty-fold reduction in systematic uncertainty to . A seven-fold improvement in clock stability, reaching for an averaging time in seconds, allows the clock to average to its systematic uncertainty in under 10 min. We improve the systematic uncertainty budget in several important ways. This includes a novel scheme for taming blackbody radiation-induced frequency shifts through active stabilization and characterization of the thermal environment, inclusion of higher-order terms in the lattice light shift, and updated atomic coefficients. Along with careful control of other systematic effects, we achieve low temporal drift of systematic offsets and high uptime of the clock. We additionally present an improved evaluation of the second order Zeeman coefficient that is applicable to all Sr optical lattice clocks. These improvements in performance have enabled several important studies including frequency ratio measurements through the boulder area clock optical network (BACON), a high precision comparison with the JILA 3D lattice clock, a demonstration of a new all-optical time scale combining SrI and a cryogenic silicon cavity, and a high sensitivity search for ultralight scalar dark matter.

Selection imposed by local environmental conditions drives differences in microbial community composition across geographically distinct groundwater aquifers.

ABSTRACTSeveral studies have analyzed biogeographic distribution patterns of microbial communities across broad spatial scales. However, it is often unclear to what extent differences in community composition across different regions are caused by dispersal limitation or selection, and if selection is caused by local environmental conditions alone or additional broad-scale region-specific factors. This is especially true for groundwater environments, which have been understudied in this context relative to other non-subsurface habitats. Here, we analyzed microbial community composition based on exact 16S rRNA amplicon sequence variants (ASVs) from four geographically separated aquifers located in different regions along a latitudinal transect of ∼700 km across Germany. Using a combination of variation partitioning and ecological null models revealed that differences in microbial community composition were mainly the product of selection imposed by local environmental conditions and to a smaller but still significant extent dispersal limitation and drift across regions. Only ∼23% of the total variation in microbial community composition remained unexplained, possibly due to underestimated effects of dispersal limitation among local communities within regions and temporal drift. No evidence was found for selection due to region-specific factors independent of local environmental conditions.

Reduction of Screening Current-Induced Field in a REBCO Coil Wound by Solder-Square-Stacked Wire

REBa 2 Ca 3 O 7-x (REBCO, RE = rare earth) coated conductors are promising conductors for high magnetic field magnet applications. For REBCO magnets, the tape structures and their superconductive characteristic cause a persistent screening current flowing in the tapes. Due to the existence of the screening current induced field (SCIF), the overall magnetic field becomes unstable and shows a temporal drift. This problem limits the application of REBCO in high-precision magnets, such as MRI and NMR. In this paper, the soldered-stacked-square (3S) REBCO wire is proposed to reduce SCIF. To confirm the reduction effect, a solenoid coil and a benchmark coil were wound by the 3S wire and the commercial 5-mm-wide REBCO tape, respectively. The screening current distributions of 3S wire and 5-mm tape were analyzed. Then, the temporal drift of the overall magnetic field and SCIF hysteresis loop were both experimentally measured for comparison. The test results showed that the 3S wire can significantly reduce the negative effects of SCIF.

Sensitivity Analysis of Factors Affecting the Calibration of Heat-Flow-Meter Apparatus

Abstract The analysis and results of a sensitivity study of four procedural variables on the calibration response of two commercial heat-flow-meter apparatuses in conformance with ASTM Test Method C518, Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus, are presented. The apparatuses ranged in plate size from 305 mm by 305 mm to 610 mm by 610 mm and were calibrated using Standard Reference Materials 1450c, Fibrous Glass Board, and 1453, Expanded Polystyrene Board, issued by the National Institute of Standards and Technology. A major objective of the study is to rank the relative importance of the factors and interactions affecting the calibration of the apparatus. Seventy-six runs were conducted under input conditions that varied the mean temperatures from 17°C to 30°C, temperature differences from 17 K to 30 K, heat flow up or down across the specimen thickness, and different circulation bath temperatures. For each apparatus and SRM, the experiment followed a full factorial design for the four factors and included three interspatial replicates to assess for temporal drift. The study revealed that mean temperature and heat flow direction were the two most important test method factors affecting the calibration of both apparatuses. Although the temperature effect was the same for both apparatuses, the heat flow direction effect was found to be instrument dependent. The study also found that the calibration factor for each apparatus was affected by the reference material utilized for calibration. Empirically derived predictive models for each apparatus SRM combination are presented covering the experimental region defined by the input test conditions.

In a Temporally Segmented Experience Hippocampal Neurons Represent Temporally Drifting Context But Not Discrete Segments.

There is widespread agreement that episodic memory is organized into a timeline of past experiences. Recent work suggests that the hippocampus may parse the flow of experience into discrete episodes separated by event boundaries. A complementary body of work suggests that context changes gradually as experience unfolds. We recorded from hippocampal neurons as male Long-Evans rats performed 6 blocks of an object discrimination task in sets of 15 trials. Each block was separated by removal from the testing chamber for a delay to enable segmentation. The reward contingency reversed from one block to the next to incentivize segmentation. We expected animals to hold two distinct, recurring representations of context to match the two distinct rule contingencies. Instead, we found that overtrained rats began each block neither above nor below chance but by guessing randomly. While many units had clear firing fields selective to the conjunction of objects in places, a significant population also reflected a continuously drifting code both within block and across blocks. Despite clear boundaries between blocks, we saw no neural evidence for event segmentation in this experiment. Rather, the hippocampal ensemble drifted continuously across time. This continuous drift in the neural representation was consistent with the lack of segmentation observed in behavior.SIGNIFICANCE STATEMENT The neuroscience literature yet to reach consensus on how the hippocampus supports the organization of events across time in episodic memory. Initial studies reported stable hippocampal maps segmented by remapping events. However, it remains unclear whether segmentation is an artifact of cue responsivity. Recently, research has shown that the hippocampal code exhibits continuous drift. Drift may represent a continually evolving context; however, it is unclear whether this is an artifact of changing experiences. We recorded dCA1 in rats performing an object discrimination task designed to segment time. Overtrained rats could not anticipate upcoming context switches but used context boundaries to their advantage. Hippocampal ensembles showed neither evidence of alternating between stable contexts nor sensitivity to boundaries, but showed robust temporal drift.

Robust, Synchronous Optical Buffer, and Logic Operation in Dual-Pump Kerr Micro-Resonator

Temporal cavity solitons (CSs) have been proposed to store the information in the form of optical bits in a single-pump Kerr micro-resonator. However, such optical buffers (OBs) realized using a single-pump are essentially asynchronous in nature. In this paper, we show that dual-pump scheme can lead to both synchronous and robust OB. Numerical simulations reveal the resilience in the performance of the OB against the writing jitters and third-order dispersion induced temporal drift. The impact of nonideal operating conditions, such as unequal pump amplitudes and pump detuning mismatch on the performance of the synchronous OB, are evaluated and the robustness of the OB with respect to these aspects are explored both analytically and numerically. As an interesting application of the proposed dual-pump scheme, we have demonstrated the capability to perform simultaneous logic operations (AND, OR) of the proposed device. All the conclusions are supported by analytical and semi-analytical approaches.

Road Drift

“Road Drift” has been conceived as a counterpart to “Road Rumour: Ground Plans for the Sky Blue City” which appeared in Performance Research journal's centenary edition (23.4/5, 2018). This fictional piece presented an anonymous document – a text + image montage – entitled ‘Bare City: We’ll Live and Die in These Towns’ which envisaged the fantasy of Coventry's ring-road being converted into a traffic-free pedestrian eco-zone, incorporating pop-up facilities, open markets, artworks etc. – above all somewhere that would not only lure suburban citizens into the centre but encourage them to interact and relish being there, and therefore linger (in the best tradition of Jan Gehl). The overall aim of these two complementary items is, first, to track urban entropies and, second, galvanise urban change. Where “Road Rumour” sought, as a fictional projection into the future, to address the latter, offering a utopian possibility in the ‘subjunctive mood’, “Road Drift” will concern itself more with the former, presenting a dystopian view in the ‘disjunctive mood’. It too bases itself on the discovery of an anonymous document, this time entitled ‘Dysjunction: these Towns will Live and Die’. It is a mapping that seeks to document a residual temporal drift, confronting the reality of the present – what the then-becoming post-war city has become – with the recent past: what future or ‘tomorrow’ was being dreamed of, or up, for the becoming city in the heady era of 1950s and 1960s civic planning and rebuilding. Focusing on one junction in particular, the montage records a drift but not that of the pedestrian or, indeed, Situationist “small group of adepts” in the city; rather it is the drift of a road in time and space and, by figurative extension, the drift of the city itself.

Influences of high-order dispersion on temporal and spectral properties of microcavity solitons.

We theoretically and numerically investigate the effects of high-order dispersion (HOD) on microcavity solitons, both in time and frequency domain with an extended normalized Lugiato-Lefever equation (LLE). The observed temporal drift of bright and dark solitons is shown to originate from high-odd-order dispersion, while the sign determines the direction of soliton movement and the amplitude decides the drift speed. HOD can also be introduced to stabilize the breathing bright and dark cavity solitons. In spectral domain, the nonlinear symmetry breaking is mainly introduced by third-order dispersion, whereas both third- and fourth-order dispersion can introduce dispersive wave accompanied by soliton tail oscillation. This work could give insight for exploring detailed intracavity pulse dynamics and spectral characteristics of Kerr combs influenced by HOD, as well as provide a viable route to delicate control of Kerr comb generation through tailoring the dispersion parameters.

Unmanned aerial vehicle-based monitoring of groundwater inputs to surface waters using an economical thermal infrared camera

Groundwater discharge into streams helps maintain flows during droughts and provides refugia for thermally sensitive species, as the relatively constant temperature of spring water buffers against instream diurnal and seasonal fluctuations. Unmanned aerial vehicle (UAV)-based thermal imagery represents an attractive option to monitor sites of groundwater-surface water mixing. However, the use of economical thermal sensors presents several challenges to obtaining a stable dataset for mosaicking. Here, we present a method for acquiring and postprocessing thermal infrared imagery at spring discharge sites using an inexpensive, uncooled microbolometer mounted on a small UAV. The procedure involves initial estimation and removal of pixel bias from the sensor output, and then compensation for temporal sensor drift by optimizing the stability of the signal at ground features detected within multiple frames. We illustrate this approach by presenting a case study at the Devils River, a groundwater dependent stream in Texas. Comparison with imagery acquired using a more expensive thermal camera system, designed to compensate for sensor drift at the time of data acquisition using knowledge of internal camera temperature, reveals that our method produces a more consistent final mosaic image. A good linear fit (r2 = 0.97) between the signal in the stabilized dataset and ground-based measurements of water temperature underscores the potential for this method to inexpensively produce high quality maps of surface temperature in ecologically important stream reaches.

High-reflectivity electromagnetic two-axis microscanner using dielectric multi-layer reflective surface

A high-reflectivity electromagnetic two-axis microscanner is presented, which uses dielectric multi-layer coating on the aluminum film at the reflective surface. The microscanner is driven biaxially with the torque generated between the radially directed magnetic field and the current path through a single-turn copper coil patterned on the scanner. To enhance reflectivity, dielectric multi-layers of Al2O3 and TiO2 films are coated on the aluminum reflective surface of the mirror. A reflectance of 96.31% was obtained by using two pairs of dielectric films at a wavelength of 850 nm. Laser irradiation tests were performed to measure the operational reliability of the microscanner. The temporal drift of the optical scan angle for the mirror with two pairs of dielectric layers was measured to be 0.16° during a 6-h operation using a femtosecond pulsed laser irradiation with an average power of 2.3 W and a high repetition rate of 80 MHz. However, for the mirror where the reflection surface was coated with an aluminum layer only, a 1.74° degradation of the tilting angle was observed.

A Waveform Archiving System for the GE Solar 8000i Bedside Monitor.

Our objective was to develop, deploy, and test a data-acquisition system for the reliable and robust archiving of high-resolution physiological waveform data from a variety of bedside monitoring devices, including the GE Solar 8000i patient monitor, and for the logging of ancillary clinical and demographic information. The data-acquisition system consists of a computer-based archiving unit and a GE Tram Rac 4A that connects to the GE Solar 8000i monitor. Standard physiological front-end sensors connect directly to the Tram Rac, which serves as a port replicator for the GE monitor and provides access to these waveform signals through an analog data interface. Together with the GE monitoring data streams, we simultaneously collect the cerebral blood flow velocity envelope from a transcranial Doppler ultrasound system and a non-invasive arterial blood pressure waveform along a common time axis. All waveform signals are digitized and archived through a LabView-controlled interface that also allows for the logging of relevant meta-data such as clinical and patient demographic information. The acquisition system was certified for hospital use by the clinical engineering team at Boston Medical Center, Boston, MA, USA. Over a 12-month period, we collected 57 datasets from 11 neuro-ICU patients. The system provided reliable and failure-free waveform archiving. We measured an average temporal drift between waveforms from different monitoring devices of 1 ms every 66 min of recorded data. The waveform acquisition system allows for robust real-time data acquisition, processing, and archiving of waveforms. The temporal drift between waveforms archived from different devices is entirely negligible, even for long-term recording.

Impact of Postsynthetic Surface Modification on Photoluminescence Intermittency in Formamidinium Lead Bromide Perovskite Nanocrystals.

We study the origin of photoluminescence (PL) intermittency in formamidinium lead bromide (FAPbBr3, FA = HC(NH2)2) nanocrystals and the impact of postsynthetic surface treatments on the PL intermittency. Single-dot spectroscopy revealed the existence of different individual nanocrystals exhibiting either a blinking (binary on-off switching) or flickering (gradual undulation) behavior of the PL intermittency. Although the PL lifetimes of blinking nanocrystals clearly correlate with the individual absorption cross sections, those of flickering nanocrystals show no correlation with the absorption cross sections. This indicates that flickering has an extrinsic origin, which is in contrast to blinking. We demonstrate that the postsynthetic surface treatment with sodium thiocyanate improves the PL quantum yields and completely suppresses the flickering, while it has no significant effect on the blinking behavior. We conclude that the blinking is caused by Auger recombination of charged excitons, and the flickering is due to a temporal drift of the exciton recombination rate induced by surface-trapped electrons.

Experimental study of the effect of the current sweep cycle on the magnetic field stability of a REBCO coil

This paper reports the effects of a current sweep cycle method on reducing the screening current induced field (SCF) in a (RE)Ba2Cu3Ox (REBCO) coil. The screening current induced field in a REBCO coil causes two major problems: temporal magnetic field drift and a reduction of the central magnetic field. This is a critical problem in relation to REBCO coils, which require a homogeneous and stable magnetic field, during, for instance, nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) applications (Itoh et al., 2013; Hemmi et al., 2005; Hahn et al., 2008; Amemiya et al., 2008; Otsuka et al., 2011; Yang et al., 2013; Ahn et al., 2009; Koyama et al., 2009; Kajikawa et al., 2015). In an effort to circumvent the SCF problem, the current sweep cycle method is investigated based on experiments in this study. The experimental results show that a greater SCF reduction in a REBCO coil can be obtained by increasing the overshooting of the current sweep cycle.

Reconstruction of Landsat time series in the presence of irregular and sparse observations: Development and assessment in north-eastern Alberta, Canada

Time series analysis of Landsat is limited by sparse and irregular sampling of clear-sky observations due to acquisition limitations, clouds, shadows, atmosphere, and sensor artifacts. Many remote sensing applications utilizing coarse spatial resolution time series methods are not suitable for Landsat due to observation sparsity. In this research we develop an imputation based approach to constrain the harmonic modeling method of Zhu et al. (2012, 2015) and Zhu and Woodcock (2014b) to reconstruct Landsat time series at a regular temporal interval. The approach was assessed for a boreal forest region in central Canada for different sparsity conditions. The imputed Landsat estimates for a specific pixel were predicted from climate or AVHRR data. These estimates were given a small weight relative to available Landsat observations in fitting the final harmonic model essentially constraining it to a more plausible range. In addition we implemented the model in a piecewise manner to handle non-linear temporal drift related to factors such as climate change, drought, or the allometric nature of vegetation regrowth. Results show that the inclusion of imputed estimates improved model predictions in the presence of observation sparsity. Where there were less than 3 observations within ±20days the imputation approach performed better, with a reduction in average reflectance error of 0.001 to 2.5. Error assessment with hold out observations, comparison to MODIS time series, and example predicted images are presented.