Reflected Signal Research Articles

Spectral Acoustic Fingerprints of Sand and Sandstone Sea Bottoms

Modern studies which dealt with the frequency domain analysis showed that a frequency-domain approach has an essential advantage and mentioned an inner qualitative relationship between the subsurface structure and its frequency spectra. This paper deals with the acoustic spectral response of sand and sandstone sediments at the sea bottom. An acoustic data collection campaign was conducted over two sand sites and two sandstone sites. The analysis of the results shows that reflections of acoustic signals from sand and sandstone sea bottom are characterized by various spectral features in the 2.75–6.75 kHz range. The differences in acoustic response of sand and sandstone can be quantified by examining the maximal normalized reflected power, the mean frequency, and the number of crossings at different power levels. The statistical value distribution of these potential classifiers was calculated and analyzed. These classifiers, and especially the roughness of the spectrum quantified by the number of crossings parameter can give information to assess the probability for sand or sandstone based on the reflected spectra and be used for actual distinction between sand and sandstone in sub bottom profiler data collection campaigns.

Evidence for the Magnetoionic Nature of Oblique VHF Reflections from Midlatitude Sporadic-E Layers

Mid-latitude sporadic-E (Es) is an intermittent phenomenon of the lower E region of the ionosphere. Es clouds are thin, transient, and patchy layers of intense ionization, with ionization densities which can be much higher than in the background ionosphere. Oblique reflection of radio signals in the very high frequency (VHF) range is regularly supported, but the mechanism for it has never been clearly established—specular reflection, scattering, and magnetoionic double refraction have all been suggested. This article proposes using the polarization behaviour of signals reflected from intense midlatitude sporadic-E clouds as an indicator of the true reflection mechanism. Results are presented from a measurement campaign in the summer of 2018, which gathered a large amount of data at a receiving station in the UK using 50 MHz amateur radio beacons as signal sources. In all cases the signals received were elliptically polarized, despite being transmitted with linear polarization; there were also indications that polarization behaviour varied systematically with the orientation of the path to the geomagnetic field. This represents, for all the examples recorded, clear evidence that signals were reflected from midlatitude Es by magnetoionic double refraction.

An efficient analysis of oblique reflection of airborne ultrasound beams from thin membranes for gas sensing.

The use of the angular spectrum method (ASM) to simulate the reflection of airborne ultrasound beams from a thin membrane separating air from a mixture of air and another gas is examined. The main advantage of this method is its high computing speed and efficiency for practical design calculations, suitable for sensing applications. The implemented ASM code is validated against custom Rayleigh integral code in a pure propagation simulation. In addition, ultrasound beam reflection calculations using ASM with finite element numerical results and experimental measurements are compared, finding good agreement in both cases. Then, ASM is used to estimate the sensitivity of specular reflection signals to variations in the composition of the incidence medium as a function of the angle of incidence. Conditions for which a reflection signal using inexpensive commercial ultrasound emitter/receiver at 40 kHz, in a simple configuration, offer a high enough sensitivity suitable for monitoring air quality indoors are found.

Performance Analysis of Hybrid RF-Reconfigurable Intelligent Surfaces Assisted FSO Communication

Optical reconfigurable intelligent surface (ORIS) is an emerging technology that can achieve reconfigurable optical propagation environments by precisely adjusting signal's reflection and shape through a large number of passive reflecting elements. In this article, we investigate the performance of an ORIS-assisted hybrid radio frequency (RF) and free space optics (FSO) communication system. By jointly considering the physical models of ORIS, RF channel, atmospheric turbulence, and pointing error, the closed-form solutions of the system's exact outage probability, asymptotic outage probability and BER have been derived. It is shown through numerical results that the derivation results are accurate and the RF-FSO links with ORISs show a slightly worse performance than the traditional RF-FSO links. However, the performance degradation introduced by ORIS is relatively small, and at the cost of this, the FSO link obtains a higher degree of beam adjustment freedom. We can also observe that both the increase of Rice factor in RF link and the decrease of pointing error in FSO link can effectively improve the system performance. Based on theoretical analysis and simulation results, the effect of each parameter and system design have been discussed.

Aerial Reconfigurable Intelligent Surfaces Meet Mobile Edge Computing

Mobile edge computing (MEC) enables users to offload their computation-intensive and latency-sensitive tasks to edge servers. Based on MEC, users can reduce their energy consumption and guarantee latency in executing computational tasks. However, current terrestrial MEC networks have some disadvantages, such as fixed deployed infrastructure and severe signal attenuation. Recently, a new paradigm of reconfigurable intelligent surface (RIS)-assisted wireless networks has drawn extensive attention due to its low cost but high spectral and energy efficiencies. This article introduces the use of aerial RIS (ARIS) mounted on an unmanned aerial vehicle (UAV) into MEC, which achieves three-dimensional signal reflections in the uplink computation offloading. The network performance can be improved by designing the communication and computation resource allocation, the ARIS's trajectory, and the amplitudes and phase shifts of passive reflecting elements. However, there are some issues that must be addressed for the ARIS-assisted MEC, including resource allocation and trajectory design, ARIS beamforming design with imperfect channel state information, and the trade-off between the non-line-of-sight excessive path loss and the doubled path loss. This article presents the motivation, applications, challenges, and opportunities of introducing ARISs into MEC. Moreover, numerical results are provided to showcase potential performance enhancement using ARISs in MEC networks.

Theoretical and Experimental Studies of Acoustic Reflection of Bubbly Liquid in Multilayer Media

Bubbly liquids are widely present in the natural environment and industrial fields, such as seawater near the ocean bottom, the multiphase flow in petroleum reservoirs, and the blood with bubbles resulting in decompression sickness. Therefore, accurate measurement of the gas content is of great significance for hydroacoustic physics, oil and gas resources exploration, and disease prevention and diagnosis. Trace bubbles in liquids can lead to considerable changes in the acoustic properties of gas–liquid two-phase media. Acoustic measurements can therefore be applied for trace bubble detection. This study derived the reflection coefficient of acoustic waves propagating in a sandwich layering model with liquid, bubbly liquid, and liquid. The influences of gas contents on the reflection coefficient at the layer interface were analyzed based on theoretical calculations. It was revealed that the magnitude of the reflection coefficient and the frequency interval between its valleys have a quantitative correlation with the gas contents. Thus, a novel means to detect the contents of trace bubbles was proposed by evaluating the reflection coefficients. The reflection features of a thin layer with bubbly liquid were then studied through experiments. It was validated by acoustical measurements and theories that the reflection coefficient is considerably sensitive to the change of gas contents as long as the gas content is tiny. With the increasing gas content, the maximum value of the reflection coefficient increases; meanwhile, the frequency intervals between the valleys become smaller. However, when the gas content is extensive enough, e.g., greater than 1%, the effect of the change of gas content on the reflection coefficient becomes inapparent. In that case, it is not easy to measure the gas content by the acoustic reflection signals with satisfying precision. This proposed method has potential applications for the detection of trace gas bubble content in several scenarios, e.g., decompression illness prevention and diagnosis.

Application of Signal Imaging Analysis Technology in Prediction and Treatment of Water Inrush in Diversion Tunnel

A signal imaging analysis technology was proposed to accurately interpret geological radar detection images in order to address the issues of difficult interpretation of radar advance forecast images of water inrush in diversion tunnels in unfavorable geological zones and difficult detection of grouting effects in grouting circles. The waveform, amplitude, and frequency differences in the radar data among various geological bodies in the fracture development zone, broken zone, and water-rich zone can be analyzed by the signal imaging analysis technology, which can extract multiple technical parameters for comprehensive judgment and provide a foundation for the interpretation of geological radar images. In this study, signal mapping analysis technology was used to interpret the geological detection images taken in front of the tunnel face and the surrounding rock geological detection map after cement-polyvinyl alcohol grouting, respectively. The accuracy of the signal mapping analysis technology was confirmed, and the following conclusions were drawn: (1) Geographic Different geological structures, such as fissure zones, broken zones, and water-rich zones, have different reflection signal properties for radar electromagnetic waves. With the help of the image, distinct geological features can be identified and water inrush can be anticipated; (2) Electronic scanning imaging can be used to observe it. The geological radar image feedback of the grouting circle after grouting indicates that the lithology of the grouting circle is complete and the grouting reinforcement and sealing effect is good when the cement-polyvinyl alcohol slurry concretion particles are dense; (3) The numerical analysis results of the seepage field of the tunnel demonstrate that the grouting of the surrounding rock can effectively reduce water seepage and control water gushing. The study's findings offer a specific reference point for the forecasting and management of water gushing in diversion tunnels located in adverse geological regions.

Tip-induced superconductivity enhancement in single-crystalline PdSb by point-contact spectroscopy

We report our mechanical point-contact spectroscopy (MPCS) study on single-crystalline superconductor PdSb with ${T}_{c}\ensuremath{\sim}$ 1.32 K and ${\ensuremath{\mu}}_{0}{H}_{c2}(0)\ensuremath{\sim}$ 900 Oe, whose ${T}_{c}$ changes very slightly against hydrostatic pressure below 2.5 GPa. For MPCS with a soft Au tip, the Andreev reflection signals suggest the same superconducting temperature ${T}_{c}$ as in the pristine PdSb crystal and the conductance curves show a fully gapped behavior, yielding a superconducting gap value of ${\mathrm{\ensuremath{\Delta}}}_{0}=$ 0.23 meV with $2{\mathrm{\ensuremath{\Delta}}}_{0}/{k}_{\mathrm{B}}{T}_{c}\ensuremath{\sim}$ 4.25 in the strong-coupling regime. However, for MPCS with a hard W tip, an enhanced superconducting ${T}_{c}$ can be observed with a concomitant increase in the superconducting gap $\mathrm{\ensuremath{\Delta}}$ in a linear relation of 0.109 meV/kelvin, whereas $2{\mathrm{\ensuremath{\Delta}}}_{0}/{k}_{\mathrm{B}}{T}_{c}$ decreases from 4.25 to 3.5 in a negative correlation with ${T}_{c}$. From first-principles calculations, we observe a Lifshitz transition related to Pd-$4{d}_{{z}^{2}}$ orbitals under uniaxial pressure, which is absent under hydrostatic pressure. Such Lifshitz transition results in an enhanced density of states near the Fermi level $n({E}_{F})$, which is in line with the enhanced ${T}_{c}$. In addition, a soft phonon mode at $H$ is hardened under uniaxial pressure, suggesting a reduced coupling strength in this case. Such local strain effect provides a natural explanation for our MPCS results on PdSb.

Bias correction of Sentinel-2 with unmanned aerial vehicle multispectral data for use in monitoring walnut fruit forest in western Tien Shan, Kyrgyzstan

The scope of our work is to compare Sentinel-2 and unmanned aerial vehicles (UAV) imagery from Western Tian Shan for monitoring applications in walnut fruit forests. Because acquiring field data on walnut fruit forests is difficult due to access limitations in the Tian Shan, remote sensing offers a unique opportunity to increase spatial and temporal coverage of ecological parameters. Sentinel-2 satellites launched in 2015 have been providing images at spatial resolutions of 10 to 20 m; however, difficulties remain as information retrieved from Sentinel pixels result from a mixture of objects that affect reflectance signals. We used submeter multispectral UAV images to assess the sensitivity of Sentinel-2 normalized difference vegetation index (NDVI) to subpixel vegetation. Results showed that Sentinel-2 data overestimates NDVI in regions with open terrain and grass, and underestimates NDVI in areas with trees. By implementing a bias correction method, the accuracy of the Sentinel-2 derived NDVI increased; R2 values increased from 0.59 to 0.88 (p value < 0.001). We also showed that drought index derived from Sentinel-2 vegetation condition index (VCI) is well correlated with the ground-based standard precipitation index (SPI). Using this bias correction method, on average the correlation increased by 3% between VCI and SPI.

Coherent Phonons in Antimony: An Undergraduate Physical Chemistry Solid-State Ultrafast Laser Spectroscopy Experiment

Ultrafast laser pump-probe spectroscopy is an important and growing field of physical chemistry that allows the measurement of chemical dynamics on their natural timescales, but undergraduate laboratory courses lack examples of such spectroscopy and the interpretation of the dynamics that occur. Here we develop and implement an ultrafast pump-probe spectroscopy experiment for the undergraduate physical chemistry laboratory course at the University of California Berkeley. The goal of the experiment is to expose students to concepts in solid-state chemistry and ultrafast spectroscopy via classic coherent phonon dynamics principles developed by researchers over multiple decades. The experiment utilizes a modern high-repetition rate 800 nm femtosecond Ti:Sapphire laser, split pulses with a variable time delay, and sensitive detection of transient reflectivity signals. The experiment involves minimal intervention from students and is therefore easy and safe to implement in the laboratory. Students first perform an intensity autocorrelation measurement on the femtosecond laser pulses to obtain their temporal duration. Then, students measure the pump-probe reflectivity of a single-crystal antimony sample to determine the period of coherent phonon oscillations initiated by an ultrafast pulse excitation, which is analyzed by fitting to a sine wave. Due to the disruption of in-person instruction caused by the COVID-19 pandemic, during those semesters students were provided the data they would have obtained during the experiment to analyze at home. Evaluation of student written reports reveals that the learning goals were met, and that students gained an appreciation for the field of ultrafast laser-induced chemistry.

Specificity of Individual Response Radial Increment of Scots Pine in the Voronezh Biosphere Reserve on the Differentiated Forest Conditions.

The purpose of our study was to assess the individual variability of the response to climatic conditions of the radial increment of Pinus sylvestris L. trees aged 100-140 years. The studied pine stand grows in the conditions of a site with a heterogeneous microrelief in the Voronezh Reserve. The calculated coefficients of synchronicity and correlation of radial increment of a sample of individual Scots pine trees (wood cores). It has been established that in the radial increment of pine trees in the Voronezh Reserve, there is a significant diversity in the reflection of the climatic signal, which, as a rule, manifests itself in certain years that are not extreme in terms of climatic conditions. The reasons for the differentiated reaction of trees to climate are the differentiated conditions of the microrelief, and also, probably, the genetic diversity of forest stands. In natural stands there are individual trees showing very low values of synchronicity coefficients (GLK, %) or correlation coefficients (CC, %) with stand average values. Intrapopulation differences in the response of pine forest stands to fluctuations in climatic factors are one of the forms of protective mechanisms for the survival of a species that have developed as a result of evolutionary development. As our study showed, intrapopulation differences are large in stands of natural origin and not subject to anthropogenic impacts.

Electromagnetic ultrasonic signal processing and imaging for debonding detection of bonded structures

This paper investigates an electromagnetic ultrasonic method for debonding detection of adhesive structures. Considering the non-stationary and nonlinear characteristics of the electromagnetic ultrasonic reflection signals, a joint adaptive noise reduction and reconstruction (JANRR) method, namely, complete ensemble empirical mode decomposition(CEEMDAN) and singular spectrum analysis(SSA) based on continuous mean square Error(CMSE) are proposed, in which, mirror extension is used to suppress the endpoint effect of decomposition, and the order of SSA noise reduction is determined based on singular entropy theory. For two side debonding detection of the adhesive layer, a back propagation (BP) neural network classification model is developed, and five characteristics such as signal skewness factor are taken as the network inputs based on Chi square test. Experiments were carried out for validation, which show that the proposed method can distinguish both signals of the upper and lower interfaces of the adhesive layer under different bonding states.

The observation of anterior segment in children with an R124L mutation corneal dystrophy by anterior segment optical coherence tomography and in vivo confocal microscopy.

To evaluate the anterior segment in children with an R124L mutation corneal dystrophy (CD) using anterior segment optical coherence tomography (AS-OCT) and in vivo confocal microscopy (IVCM). We investigated a family with prevalent CD and an R124L mutation; 59 individuals (14 patients; 6 male and 8 female, aged 2-69 years, 6 children, 2:4 male: female ratio) from four generations were included. We observed corneal lesions through ophthalmologic examinations, AS-OCT, and IVCM. The mean follow-up was 4.60 ± 3.91 years. The mean age for childhood CD onset was 0.90 ± 0.61 years. An Avelino DNA test revealed a heterozygous R124L mutation. Clinical manifestations included recurrent photophobia, tearing, and a foreign body sensation. Recurrence frequency decreased with age. Slit lamp microscopy revealed a rough corneal epithelium. The anterior matrix under the corneal epithelium and the anterior elastic layer were scattered with gray and white opacity. From onset to follow-up, the children's visual acuity decreased from 0.34 ± 0.12 to 0.55 ± 0.17 LogMAR units. AS-OCT showed uneven corneal epithelial thickness. The Bowman's layer was replaced by abnormal substances in the anterior segment. Corneal deposits became increasingly thicker; the average thickness at the last follow-up was 102.78 ± 10.13 μm. IVCM revealed uneven and reflective signals in the corneal upper cortex and subepithelium, with unclear boundaries and a loss of normal cell morphology. We report an early age of onset in a family with prevalent CD due to R124L mutations. AS-OCT is a convenient, quick, and non-contact tool for screening and monitoring the pathological process of CD.

Denoising of distributed acoustic sensing data using supervised deep learning

Distributed acoustic sensing (DAS) is an emerging technology for acquiring seismic data due to its high-density and low-cost advantages. Because of the harsh acquisition environment and other unexpected reasons, the seismic signals acquired in DAS are masked by various types of complex noise, which seriously decreases the signal-to-noise ratio of seismic data. We propose a fully convolutional neural network with dense and residual connections to attenuate complex noise in DAS data. The network is designed to learn features of useful reflection signals recorded from a large number of earthquake and microseismic events, aiming at obtaining an unprecedented generalization ability. First, we generate labels using an integrated framework that attenuates specific types of noise in real DAS data, where the integrated framework includes carefully designed band-pass, structure-oriented median, and dip filters. Then, we use the patching technique to segment the training samples into many small-scale patches to reduce computational cost and improve the extraction of essential features from large-scale passive seismic data. Finally, we use the well-trained network to estimate the heavily polluted hidden signals. Compared with two advanced deep-learning methods and a traditional denoising framework, our proposed method can more effectively attenuate strong and complex noise and recover weak hidden signals in synthetic and real DAS data tests.

High-spatial-resolution OFDR with single interferometer using self-compensation method

A high-spatial-resolution optical frequency domain reflectometry (OFDR) with single interferometer was proposed by using self-compensation method (SCM). The auxiliary interferometer (AI) of conventional OFDR was replaced by a processed arc end of the fiber under test (FUT) to generate a reflection signal with appropriate intensity. The actual instantaneous optical frequency (IOF) was successfully extracted from the arc end of the FUT. Combining the arc end and SCM, the phase noise of the proposed OFDR was successfully eliminated to obtain the compensated signal with high signal-to-noise ratio (SNR). Moreover, the influence of delay fiber (DF) length on the compensation effect was theoretically and experimentally analyzed. The proposed OFDR achieved the distributed temperature sensing with a high-spatial-resolution of 3 mm without sacrificing measurement performance, where the measured distance of the FUT was ∼ 108 m. The high-spatial-resolution of 5 mm was still achieved when the measured distance of the FUT was increased to ∼170 m. Such an OFDR system with low cost and good performance has development potential in the field of distributed measurement.

Application of Hilbert instantaneous spectrum on improved bolt anchoring quality detection

AbstractThe nondestructive testing technology for bolt anchoring quality based on the acoustic reflection method is developing rapidly. Hilbert transform instantaneous spectrum is frequently used. However, due to the existence of the folding phenomenon in the instantaneous phase, the accurate identification of reflected signal and the effective calculation of the anchorage compactness remain a challenge. The instantaneous frequency curve of the bolt signal is used to overcome the phase folding problem. The instantaneous frequency curve of the signal can help accurately identify the reflected signal from the bolt bottom and the position of the defect, thus accurately calculate the length of the bolt and the position of the defect. According to the analysis of the instantaneous amplitude curve of the signal, the formula for computing the bolt anchorage compactness is derived based on the correlation between the attenuation amplitude ratio of the reflected signal and the bolt anchoring quality. Research results show that difficult problems such as bolt reflection signal identification and anchorage compactness calculation are both effectively solved. The model simulation analyzes and field application examples verify the effectiveness and practicability of the methodology, which provides a robust way for the nondestructive testing of the bolt anchoring quality.

A novel red‐edge spectral index for retrieving the leaf chlorophyll content

Abstract The leaf chlorophyll content (Chlleaf) is a crucial vegetation parameter in carbon cycle modelling and agricultural monitoring at local, regional and global scales. The red‐edge spectral region is sensitive to variations in Chlleaf. An increasing number of sensors are capable of sampling red‐edge bands, providing opportunities to estimate Chlleaf. However, the contributions of canopy/foliar/soil factors are always combined in the reflectance signal, which limits the generalizability of vegetation index (VI)‐based Chlleaf inversions. This study aims to propose a new red‐edge chlorophyll index to decouple the effects of the canopy and soil background from the Chlleaf estimation. The chlorophyll sensitive index (CSI) was proposed, and the regression equations between the CSI and Chlleaf were acquired using PROSAIL (PROSPECT + SAIL) and the 4‐Scale‐PROSPECT model. Sensitivity analyses showed that the CSI is resistant to variations in the canopy structure and soil background. Validation results obtained using 308 ground‐measured samples over nine sites world‐wide revealed that CSI improves the Chlleaf retrieval accuracy (root mean square error (RMSE = 9.39 μg cm−2) compared with the existing Medium Resolution Imaging Spectrometer (MERIS) terrestrial chlorophyll index (MTCI; RMSE = 13.00 μg cm−2). Moreover, the CSI method steadily achieves a highly accurate inversion under different LAI and Chlleaf conditions. Based on the CSI regression method, a Chlleaf product with a 30‐m/10‐day resolution across China was generated. The CSI is sensitive to Chlleaf but resistant to canopy structure and soil moisture parameters, and it has the potential to explicitly retrieve leaf‐scale biochemistry in ecosystem modelling and ecological applications.

Coastal tides measurement in Indonesia using GNSS-Reflectometry

The important role of coastal areas in human life and their vulnerability to natural hazards such as sea level rise, make continuous monitoring of coastal ecosystem rehabilitation concerning the local sea level is urgently required. Conventional tide observation using a tide gauge sensor measures a local sea level relative to the land. Unfortunately, the effects of deformation and land subsidence around tidal stations make local tide observations irrelevant to measure absolute sea level rise. Currently, an alternative method is being developed accordingly. The method utilizes Global Navigation Satellite Systems (GNSS) signal, known as GNSS-Reflectometry (GNSS-R), to observe the tide. This research aimed to observe the sea level from the reflection of the GNSS signal. Tidal observation using GNSS-R was carried out in four Geospatial Information Agency’s tidal stations, i.e., Morotai, Piru, Tehoru, and Pasangkayu. The tide was determined based on the dominant frequency of a multipath signal, which is obtained by separating the composite signal from the direct one using 3rd order polynomial fitting. The combination of GPS and GLONASS at the L1 and L2 frequencies resulted in tide observations with an RMSE value of 18 cm. The result is 90% correlated with tidal observation using tide gauge sensor. The residual of main tidal constituent vector in both semidiurnal and diurnal components ranged from 0.01 to 0.02 m. This means that the tide prediction generated from the GNSS-R observation is statistically similar to the prediction generated from the tide gauge sensor.

Path Loss Measurements and Model Analysis in an Indoor Corridor Environment at 28 GHz and 38 GHz.

This paper examines the large-scale path loss models for an indoor corridor environment at frequencies of 28 and 38 GHz. The measurement environment consists of an indoor corridor with both line-of-sight (LOS) and non-line of sight (NLOS) scenarios using vertical–vertical (V–V) and vertical–horizontal (V–H) antenna polarizations. The single-frequency close-in (CI), floating intercept (FI), free space large-scale path loss models and measured data from the measurement campaign were used to evaluate the performance analysis. The paper also focuses on various parameters, such as standard deviation, path loss exponent (PLE), accuracy, simplicity, and stability of the models. The analysis focuses on the peculiarity of the effect of the wall proximity on the path loss parameters as well as comparisons with the parameters in some of the reviewed literature studies. The FI and CI models produce comparable results for both antenna polarizations and clearly fit with the measured path loss. The PLE, with the highest value of 3.33 at 38 GHz (V–H), is much higher in the NLOS scenario with V–H polarization due to the signal degradation along the path from the transmitter (Tx) to the receiver (Rx). This is because there is no direct LOS between the Tx and Rx antennas. The Rx only relies on signal diffractions and reflections from obstacles as it transmits through the path from the Tx antenna. The path loss measurements and model analysis presented here are useful in designing 5G wireless communication systems for indoor environments, particularly for power budget calculations.

Spectral reflection and crop parameters: can the disentanglement of primary and secondary traits lead to more robust and extensible prediction models?

Recently the application of spectral reflection data for the prediction of crop parameters for applications in precision agriculture, such as green area index (GAI), total aboveground dry matter (DM), and total aboveground nitrogen content (N content) increases. However, the usability of vegetation indices (VI) for the prediction of crop parameters is strongly limited by the fact that most VI calibrations are only valid for specific crops and growth periods. The results of the presented study based on the differentiation of primary (main driver of the reflectance signal) and secondary (not directly related to reflectance signal) crop parameters. For GAI prediction, a universal (without crop-specific parametrization) simple ratio vegetation index (SR) provided good calibration (R2 adj. = 0.90, MAE = 0.32, rMAE = 22%) and evaluation results (MAE = 0.33, rMAE = 18%). The disentanglement of primary and secondary traits allowed the development of a functional two-step model for the estimation of the N content during vegetative growth (MAE = 19.2 g N m−1, rMAE = 44%). This model was based on fundamental, crop-specific relationships between the crop parameters GAI and N content. Additionally, an advanced functional approach was tested enabling the whole-season prediction of DM and confirming a reliable GAI estimation throughout the whole growing season (R2 = 0.89–0.93).