6 research outputs found
Characterizing uncertainty in process-based hydraulic modeling, exemplified in a semiarid Inner Mongolia steppe
Assessing root sources of three uncertainties – parameterization of soil hydraulic characteristics, boundary conditions, and estimation of source/sink terms – is a significant challenge in soil water transport modeling. This study aims to evaluate the uncertainty of three each widely-used parameter estimation methods affecting plot-scale water dynamics. The study employs HYDRUS, a process-based hydrologic model, to incorporate these uncertainties and compare model predictions to measured values in a semiarid Inner Mongolia steppe, China. Soil hydraulic parameters are determined using two direct methods (laboratory-derived approach and evaporation method) and one indirect method (neural network). While each hydraulic parameter method generally simulates soil moisture dynamics, the evaporation method performed better, especially under dry conditions. This suggests that measuring the intensity properties, such as unsaturated hydraulic conductivity, with the evaporation method is crucial for reasonable soil moisture simulation. The study also demonstrates the impact of different applied boundary conditions on simulated soil moisture, specifically the partitioning of reference FAO evapotranspiration via one direct method (soil fraction cover) and two indirect methods (leaf area index and crop height). The partitioning via soil fraction cover reflected a better simulation. Additionally, the study compares the uncertainties of root water uptake function with root growth parameters and constant root depth referenced to grass and pasture, and finds no significant difference among them. Comparing three sources of uncertainty in predicting soil moisture, the study concludes that the input soil hydraulic parameter is more sensitive than evapotranspiration partitioning or representation of root water uptake function. Our study highlights that measuring soil intensity properties can better reflect the effects of land use change, such as compaction, on field water transports
Measurement of the vertical atmospheric density profile from the X-ray Earth occultation of the Crab Nebula with Insight-HXMT
In this paper, the X-ray Earth occultation (XEO) of the Crab Nebula is
investigated by using the Hard X-ray Modulation Telescope (Insight-HXMT). The
pointing observation data on the 30th September, 2018 recorded by the Low
Energy X-ray telescope (LE) of Insight-HXMT are selected and analyzed. The
extinction lightcurves and spectra during the X-ray Earth occultation process
are extracted. A forward model for the XEO lightcurve is established and the
theoretical observational signal for lightcurve is predicted. The atmospheric
density model is built with a scale factor to the commonly used MSIS density
profile within a certain altitude range. A Bayesian data analysis method is
developed for the XEO lightcurve modeling and the atmospheric density
retrieval. The posterior probability distribution of the model parameters is
derived through the Markov Chain Monte Carlo (MCMC) algorithm with the
NRLMSISE-00 model and the NRLMSIS 2.0 model as basis functions and the best-fit
density profiles are retrieved respectively. It is found that in the altitude
range of 105--200 km, the retrieved density profile is 88.8% of the density of
NRLMSISE-00 and 109.7% of the density of NRLMSIS 2.0 by fitting the lightcurve
in the energy range of 1.0--2.5 keV based on XEOS method. In the altitude range
of 95--125 km, the retrieved density profile is 81.0% of the density of
NRLMSISE-00 and 92.3% of the density of NRLMSIS 2.0 by fitting the lightcurve
in the energy range of 2.5--6.0 keV based on XEOS method. In the altitude range
of 85--110 km, the retrieved density profile is 87.7% of the density of
NRLMSISE-00 and 101.4% of the density of NRLMSIS 2.0 by fitting the lightcurve
in the energy range of 6.0--10.0 keV based on XEOS method. This study
demonstrates that the XEOS from the X-ray astronomical satellite Insight-HXMT
can provide an approach for the study of the upper atmosphere.Comment: 31 pages, 15 figures, 5 tables, accepted for publication in
Atmospheric Measurement Technique
Insight-HXMT dedicated 33-day observation of SGR J1935+2154 I. Burst Catalog
Magnetars are neutron stars with extreme magnetic field and sometimes
manifest as soft gamma-ray repeaters (SGRs). SGR J1935+2154 is one of the most
prolific bursters and the first confirmed source of fast radio burst (i.e. FRB
200428). Encouraged by the discovery of the first X-ray counterpart of FRB,
Insight-Hard X-ray Modulation Telescope (Insight-HXMT) implemented a dedicated
33-day long ToO observation of SGR J1935+2154 since April 28, 2020. With the
HE, ME, and LE telescopes, Insight-HXMT provides a thorough monitoring of burst
activity evolution of SGR J1935+2154, in a very broad energy range (1-250 keV)
with high temporal resolution and high sensitivity, resulting in a unique
valuable data set for detailed studies of SGR J1935+2154. In this work, we
conduct a comprehensive analysis of this observation including detailed burst
search, identification and temporal analyses. After carefully removing false
triggers, we find a total of 75 bursts from SGR J1935+2154, out of which 70 are
single-pulsed. The maximum burst rate is about 56 bursts/day. Both the burst
duration and the waiting time between two successive bursts follow log-normal
distributions, consistent with previous studies. We also find that bursts with
longer duration (some are multi-pulsed) tend to occur during the period with
relatively high burst rate. There is no correlation between the waiting time
and the fluence or duration of either the former or latter burst. It also seems
that there is no correlation between burst duration and hardness ratio, in
contrast to some previous reports. In addition, we do not find any X-ray burst
associated with any reported radio bursts except for FRB 200428.Comment: 31 pages, 10 figures, accepted for publication in ApJ
New method for Earth neutral atmospheric density retrieval based on energy spectrum fitting during occultation with LE/\emph{Insight}-HXMT
We propose a new method for retrieving the atmospheric number density profile
in the lower thermosphere, based on the X-ray Earth occultation of the Crab
Nebula with the Hard X-ray Modulation Telescope (\emph{Insight}-HXMT)
Satellite. The absorption and scattering of X-rays by the atmosphere result in
changes in the X-ray energy, and the Earth's neutral atmospheric number density
can be directly retrieved by fitting the observed spectrum and spectrum model
at different altitude ranges during the occultation process. The pointing
observations from LE/\emph{Insight}-HXMT on 16 November 2017 are analyzed to
obtain high-level data products such as lightcurve, energy spectrum and
detector response matrix. The results show that the retrieved results based on
the spectrum fitting in the altitude range of 90--200 km are significantly
lower than the atmospheric density obtained by the NRLMSISE-00 model,
especially in the altitude range of 110--120 km, where the retrieved results
are 34.4\% lower than the model values. The atmospheric density retrieved by
the new method is qualitatively consistent with previous independent X-ray
occultation results (Determan et al., 2007; Katsuda et al., 2021), which are
also lower than empirical model predictions. In addition, the accuracy of
atmospheric density retrieved results decreases with the increase of altitude
in the altitude range of 150--200 km, and the accurate quantitative description
will be further analyzed after analyzing a large number of X-ray occultation
data in the future.Comment: 9 pages, 6 figures, 2 tables, accepted for publication in Advances in
Space Researc
Characterizing uncertainty in process-based hydraulic modeling, exemplified in a semiarid Inner Mongolia steppe
Assessing root sources of three uncertainties – parameterization of soil hydraulic characteristics, boundary conditions, and estimation of source/sink terms – is a significant challenge in soil water transport modeling. This study aims to evaluate the uncertainty of three each widely-used parameter estimation methods affecting plot-scale water dynamics. The study employs HYDRUS, a process-based hydrologic model, to incorporate these uncertainties and compare model predictions to measured values in a semiarid Inner Mongolia steppe, China. Soil hydraulic parameters are determined using two direct methods (laboratory-derived approach and evaporation method) and one indirect method (neural network). While each hydraulic parameter method generally simulates soil moisture dynamics, the evaporation method performed better, especially under dry conditions. This suggests that measuring the intensity properties, such as unsaturated hydraulic conductivity, with the evaporation method is crucial for reasonable soil moisture simulation. The study also demonstrates the impact of different applied boundary conditions on simulated soil moisture, specifically the partitioning of reference FAO evapotranspiration via one direct method (soil fraction cover) and two indirect methods (leaf area index and crop height). The partitioning via soil fraction cover reflected a better simulation. Additionally, the study compares the uncertainties of root water uptake function with root growth parameters and constant root depth referenced to grass and pasture, and finds no significant difference among them. Comparing three sources of uncertainty in predicting soil moisture, the study concludes that the input soil hydraulic parameter is more sensitive than evapotranspiration partitioning or representation of root water uptake function. Our study highlights that measuring soil intensity properties can better reflect the effects of land use change, such as compaction, on field water transports