scholarly journals Strategies for the Efficient Estimation of Soil Moisture through Spectroscopy: Sensitive Wavelength Algorithm, Spectral Resampling and Signal-to-Noise Ratio Selection

2022 ◽  
Vol 12 (2) ◽  
pp. 826
Author(s):  
Jing Yuan ◽  
Bo Yu ◽  
Changxiang Yan ◽  
Junqiang Zhang ◽  
Ning Ding ◽  
...  

It is found that the remote sensing parameters such as spectral range, spectral resolution and signal-to-noise ratio directly affect the estimation accuracy of soil moisture content. However, the lack of research on the relationship between the parameters and estimation accuracy restricts the prolongation of application. Therefore, this study took the demand for this application as the foothold for developing spectrometry. Firstly, a method based on sensitivity analysis of soil radiative transfer model-successive projection algorithm (SA-SPA) was proposed to select sensitive wavelengths. Then, the spectral resampling method was used to select the best spectral resolution in the corresponding sensitive wavelengths. Finally, the noise-free spectral data simulated by the soil radiative transfer model was added with Gaussian random noise to change the signal-to-noise ratio, so as to explore the influence of signal-to-noise ratio on the estimation accuracy. The research results show that the estimation accuracy obtained through the SA-SPA (RMSEP < 12.1 g kg−1) is generally superior to that from full-spectrum data (RMSEP < 14 g kg−1). At selected sensitive wavelengths, the best spectral resolution is 34 nm, and the applicable signal-to-noise ratio ranges from 150 to 350. This study provides technical support for the efficient estimation of soil moisture content and the development of spectrometry, which comprehensively considers the common influence of spectral range, spectral resolution and signal-to-noise ratio on the estimation accuracy of soil moisture content.

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Rehman S. Eon ◽  
Charles M. Bachmann

AbstractThe advent of remote sensing from unmanned aerial systems (UAS) has opened the door to more affordable and effective methods of imaging and mapping of surface geophysical properties with many important applications in areas such as coastal zone management, ecology, agriculture, and defense. We describe a study to validate and improve soil moisture content retrieval and mapping from hyperspectral imagery collected by a UAS system. Our approach uses a recently developed model known as the multilayer radiative transfer model of soil reflectance (MARMIT). MARMIT partitions contributions due to water and the sediment surface into equivalent but separate layers and describes these layers using an equivalent slab model formalism. The model water layer thickness along with the fraction of wet surface become parameters that must be optimized in a calibration step, with extinction due to water absorption being applied in the model based on equivalent water layer thickness, while transmission and reflection coefficients follow the Fresnel formalism. In this work, we evaluate the model in both field settings, using UAS hyperspectral imagery, and laboratory settings, using hyperspectral spectra obtained with a goniometer. Sediment samples obtained from four different field sites representing disparate environmental settings comprised the laboratory analysis while field validation used hyperspectral UAS imagery and coordinated ground truth obtained on a barrier island shore during field campaigns in 2018 and 2019. Analysis of the most significant wavelengths for retrieval indicate a number of different wavelengths in the short-wave infra-red (SWIR) that provide accurate fits to measured soil moisture content in the laboratory with normalized root mean square error (NRMSE)< 0.145, while independent evaluation from sequestered test data from the hyperspectral UAS imagery obtained during the field campaign obtained an average NRMSE = 0.169 and median NRMSE = 0.152 in a bootstrap analysis.


Horticulturae ◽  
2021 ◽  
Vol 7 (6) ◽  
pp. 154
Author(s):  
Chen Ru ◽  
Xiaotao Hu ◽  
Wene Wang ◽  
Hui Ran ◽  
Tianyuan Song ◽  
...  

Precise irrigation management of grapevines in greenhouses requires a reliable method to easily quantify and monitor the grapevine water status to enable effective manipulation of the water stress of the plants. This study describes a study on stem diameter variations of grapevine planted in a greenhouse in the semi-arid area of Northwest China. In order to determine the applicability of signal intensity of stem diameter variation to evaluate the water status of grapevine and soil. The results showed that the relative variation curve of the grapevine stem diameter from the vegetative stage to the fruit expansion stage showed an overall increasing trend. The correlations of MDS (maximum daily shrinkage) and DI (daily increase) with meteorological factors were significant (p < 0.05), and the correlations with SWP, RWC and soil moisture were weak. Although MDS and DI can diagnose grapevine water status in time, SIMDS and SIDI have the advantages of sensitivity and signal intensity compared with other indicators. Compared with MDS and DI, the R2 values of the regression equations of SIMDS and SIDI with SWP and RWC were high, and the correlation reached a very significant level (p < 0.01). Thus, SIMDS and SIDI are more suitable for the diagnosis of grapevine water status. The SIMDS peaked at the fruit expansion stage, reaching 0.957–1.384. The signal-to-noise ratio of SIDI was higher than that of MDS across the three treatments at the vegetative stage. The value and signal-to-noise ratio of SIDI at the flowering stage were similar to those of SIMDS, while the correlation between SIDI and the soil moisture content was higher than that of SIMDS. It can be concluded that that SIDI is suitable as an indicator of water status of grapevine and soil during the vegetative and flowering stages. In addition, the signal-to-noise ratio of SIMDS during the fruit expansion and mature stages was significantly higher than that of SIDI. Therefore, SIMDS is suitable as an indicator of the moisture status of grapevine and soil during the fruit expansion and mature stages. In general, SIMDS and SIDI were very good predictors of the plant water status during the growth stage and their continuous recording offers the promising possibility of their use in automatic irrigation scheduling in grapevine.


2018 ◽  
Vol 42 (1) ◽  
pp. 167-174 ◽  
Author(s):  
V. I. Parfenov ◽  
D. Y. Golovanov

An algorithm for estimating time positions and amplitudes of a periodic pulse sequence from a small number of samples was proposed. The number of these samples was determined only by the number of pulses. The performance of this algorithm was considered on the assumption that the spectrum of the original signal is limited with an ideal low-pass filter or the Nyquist filter, and conditions for the conversion from one filter to the other were determined. The efficiency of the proposed algorithm was investigated through analyzing in which way the dispersion of estimates of time positions and amplitudes depends on the signal-to-noise ratio and on the number of pulses in the sequence. It was shown that, from this point of view, the efficiency of the algorithm decreases with increasing number of sequence pulses. Besides, the efficiency of the proposed algorithm decreases with decreasing signal-to-noise ratio.It was found that, unlike the classical maximum likelihood algorithm, the proposed algorithm does not require a search for the maximum of a multivariable function, meanwhile characteristics of the estimates are practically the same for both these methods. Also, it was shown that the estimation accuracy of the proposed algorithm can be increased by an insignificant increase in the number of signal samples.The results obtained may be used in the practical design of laser communication systems, in which the multipulse pulse-position modulation is used for message transmission. 


1971 ◽  
Vol 41 ◽  
pp. 361-362
Author(s):  
M. Combes

1.Ultraviolet spectra (1400–1800 Å) of Ap, Am and normal A stars are needed by F. Praderie, R. Bonnet and R. Cayrel.The spectral resolution has to be nearly 1 Å. Accurate relative photometry (5%) and absolute calibration (30–50%) are required.A rocket experiment, proposed to ESRO by M. Combes and P. Felenbok is planned for launch in 1972.2.As neutral silicon and magnesium are very efficient ultra-violet absorbents, A stars ultraviolet fluxes are very faint (Praderie, 1968).Then a very luminous optical set-up and a high efficiency receiver have to be used. A 30 cm in diameter concave objective grating is associated with a Lallemand electronic camera. The grating (2000 //mm; //l) is holographically made (Labeyrie, 1969). The electronic camera is electrostatically focussed. A semi-transparent solar-blind CsL photocathode is used (Carruthers, 1966).3.A little mirror, placed against the grating and forming a direct view of the sky, permits to establish an absolute wavelength scale.During the fly, before and after stellar observations, a little concave mirror mounted into the opening side-door is used to form on the photocathode a spectrum of a Deuterium calibrated lamp. Two photomultipliers, one on each side of the electronic camera, control the lamp stability.The complete mounting is calibrated in the laboratory using a thermopile as reference, before the launch and after the recovery of the waterproof payload.4.The chosen stars are the brightest Ap and Am stars: α Dra (Ap; mv = 3.64; equivalent type A 0) and α2 Lib (Am; mv = 2.75; equivalent type A3-A7).It seems to be possible to obtain spectra (1400-1800 Å) of the Ap star with a spectral resolution of 1 Å and a signal to noise ratio better than 40. But at a pinch one may accept a resolution of 2 Å and a signal to noise ratio of 15 for the shortest range of the Ap star spectrum.


2004 ◽  
Vol 22 (11) ◽  
pp. 3995-4003 ◽  
Author(s):  
V. K. Anandan ◽  
C. J. Pan ◽  
T. Rajalakshmi ◽  
G. Ramachandra Reddy

Abstract. Multitaper spectral analysis using sinusoidal taper has been carried out on the backscattered signals received from the troposphere and lower stratosphere by the Gadanki Mesosphere-Stratosphere-Troposphere (MST) radar under various conditions of the signal-to-noise ratio. Comparison of study is made with sinusoidal taper of the order of three and single tapers of Hanning and rectangular tapers, to understand the relative merits of processing under the scheme. Power spectra plots show that echoes are better identified in the case of multitaper estimation, especially in the region of a weak signal-to-noise ratio. Further analysis is carried out to obtain three lower order moments from three estimation techniques. The results show that multitaper analysis gives a better signal-to-noise ratio or higher detectability. The spectral analysis through multitaper and single tapers is subjected to study of consistency in measurements. Results show that the multitaper estimate is better consistent in Doppler measurements compared to single taper estimates. Doppler width measurements with different approaches were studied and the results show that the estimation was better in the multitaper technique in terms of temporal resolution and estimation accuracy.


2018 ◽  
Vol 8 (1) ◽  
pp. 23-29
Author(s):  
Firman Ridwan ◽  
Roni Novison

This study was aimed to improve the quality of aroma of roasted coffee by using Taguchi's design as experimental technique. The roaster parameters evaluated were temperature, incubation time, moisture content and cylinder rotational speed. An orthogonal array L9, signal to noise ratio and ANOVA were employed to investigate the influence of the roaster parameters. The results showed that the optimal roasted coffee aroma was produced at a temperature of 170◦C, incubation time of 14 minutes, moisture content of 6% (v/w) and cylinder rotational speed of 50 rpm. The most to less significant roasting parameters as observed in this study were as follows: temperature, incubation time, moisture content and cylinder rotational speed. Furthermore, the results showed that the Taguchi design was better than the full experimental design in solving experiments with a minimum number. Keywords: ANOVA, Coffee roaster, Roasted coffee aroma, Signal to noise ratio, Taguchi technique


2019 ◽  
Author(s):  
Alexander V. Rodin ◽  
Dmitry V. Churbanov ◽  
Sergei G. Zenevich ◽  
Artem Yu. Klimchuk ◽  
Vladimir M. Semenov ◽  
...  

Abstract. We propose a new technique of remote wind measurements based on Doppler analysis of a CO2 absorption line in the 1.605 μm overtone band measured in the direct Sun observation geometry. Heterodyne spectroradiometric measurements of the solar radiation passed through the atmosphere provides an unprecedented spectral resolution up to λ/δλ ~ 107–108 with a signal-to-noise ratio more than 100. The shape of the individual rotational line profile provides unambiguous relationship between offset from the line centre and altitude where a respective part of the line profile is formed. Therefore, an inverse problem may be posed in order to retrieve vertical distribution of wind, with retrievals vertical resolution compromised by a spectral resolution and signal-to-noise ratio of the measurements. A close coincidence between measured and synthetic absorption line is reached, with retrieved wind profile between the surface and 50 km being in a good agreement with reanalysis models. This method may pose an alternative to widely employed lidar and radar techniques.


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