Quantifying the amount of precipitation and its uncertainty is a challenging task all over the world, particularly over the African continent, where rain gauge (RG) networks are poorly distributed. In recent decades, several satellite remote sensing (SRS)-based precipitation products have become available with reasonable spatial and temporal resolutions to be applied in hydrological and climate studies. However, uncertainties of these products over Africa are largely unknown. In this study, the generalized ‘three-cornered-hat’ (TCH) method is applied to estimate uncertainties of gridded precipitation products over the entire African continent, without being dependent to the choice of a reference dataset. Six widely used SRS-based precipitation products (at monthly scales) were evaluated over the entire continent during the period of 2003–2010. The TCH results are further compared to those of the classical evaluation using the Global Precipitation Climatology Centre (GPCC) over entire Africa, as well as to the RG observations over the Greater Horn of Africa (GHA). Overall, for the study period (2003–2010), the TCH results indicate that the RG-merged products contain smaller error amplitudes compared to the satellite-only products, consistent with the GPCC-based evaluation. A multiple comparison procedure ranking, which was applied based on signal-to-noise ratios (SNRs), indicated that PERSIANN contains the highest SNR and thus suitable over most of Africa, followed by ARCv2, TRMM, CMORPH, TAMSAT, and GSMaP. To extract the main spatio-temporal variability of rainfall over Africa, complex empirical orthogonal function technique was applied, from which the extracted patterns of GPCC, TRMM, PERSIANN, and ARCv2 were found to be similar but different from those of TAMSAT, CMORPH, and GSMaP. Finally, the TCH and RG-based validation methods were found to provide similar evaluations for the SRS-only products (CMORPH and GSMaP) over GHA, with CMORPH emerging to be the most suitable product, consistent with previous studies.

/pdf/uncertainties-in-remotely-sensed-precipitation-data-over-18xm9ne9kq.pdf

Uncertainties in remotely sensed precipitation data over Africa

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018JD028447

Evaluating Different Machine Learning Methods for Upscaling Evapotranspiration from Flux Towers to the Regional Scale

The assessment of geoheritage is a crucial task for the establishment of ranks according to their value, an important step for the elaboration of catalogues and the implementation of protection and use programmes. One important problem that permeates the different stages of geoheritage assessment is subjectivity in the selection and application of criteria. Evaluation methods frequently used are based on the assignment of values through the expert’s judgement (direct methods). In the last few decades, parametric methods, based on the measurement of specific features of geomorphosites have been increasingly applied. This type of procedure allows different operators to obtain similar results if certain criteria are accepted, but it requires more time and effort. A parametric method is proposed here based on three sets of criteria: intrinsic quality, potential for use and protection needs. The method has been tested on a series of coastal geomorphosites. Specific criteria, parameters to express them and value ranks are proposed. A statistical approach has been applied to the criteria to identify the most significant ones and their relative weights. The analysis enabled reduction of the number of criteria, eliminating redundancies. The new set of criteria was applied to assess the value of geomorphosites located in the north of Spain. The classification was compared with the ones obtained by both the parametric method using a larger number of parameters and a direct evaluation applied to the same sites. Results show a quite good coincidence. It is concluded that this approach makes it possible to obtain reliable classifications of geomorphosites based on clearly defined criteria and replicable procedures, but with a much lower effort, using a limited number of criteria.

A Statistical Approach to the Validation and Optimisation of Geoheritage Assessment Procedures

Long-term groundwater storage variations estimated in the Songhua River Basin by using GRACE products, land surface models, and in-situ observations.

Evaluation of twelve evapotranspiration products from machine learning, remote sensing and land surface models over conterminous United States

The calibration of time transfer links is mandatory in the context of international collaboration for the realization of International Atomic Time. In this paper, we present the results of the calibration of the GPS time transfer link between the Real Instituto y Observatorio de la Armada (ROA) and the Physikalisch-Technische Bundesanstalt (PTB) by means of a traveling geodetic-type GPS receiver and an evaluation of the achieved type A and B uncertainty. The time transfer results were achieved by using CA, P3, and also carrier phase PPP comparison techniques. We finally use these results to re-calibrate the two-way satellite time and frequency transfer (TWSTFT) link between ROA and PTB, using one month of data. We show that a TWSTFT link can be calibrated by means of GPS time comparisons with an uncertainty below 2 ns, and that potentially even sub-nanosecond uncertainty can be achieved. This is a novel and cost-effective approach compared with the more common calibration using a traveling TWSTFT station.

Improved GPS-based time link calibration involving ROA and PTB

In recent years, a certain correlation detected between clocks at time and frequency laboratories has been the main reason behind the development of a revised version of the classical `Three-Cornered Hat' method as a mathematical tool to estimate the frequency instability of a set of clocks. The method has been formulated keeping in mind the possibility of dependence among clocks and has been generalized to an ensemble of N clocks [1–5]. It basically consists of the minimization of an objective function, the quadratic sum of cross-correlation coefficients, with the constraint condition established by the positive definiteness of the (estimated) absolute covariance matrix related to the clocks. Later on, a matrix formulation to calculate the optimal weights in the case of correlated clocks was presented in [6]. The impact of this weighting procedure on the instability of the ensemble time was evaluated, on the basis of simulated clocks, when correlation was appropriately taken into account and in the case when it was neglected. That paper established, as a main conclusion, the mathematical treatment to be used in the usual case of weak dependence. In this paper, we present a summary of the theory involved, and then apply the procedures to optimal weighting of clocks using real data clocks at Real Observatorio de la Armada (San Fernando, Spain). Finally, we discuss the results obtained.

http://iopscience.iop.org/article/10.1088/0026-1394/40/3/301/pdf

Post-processing ROA data clocks for optimal stability in the ensemble timescale

: The estimation of individual instabilities of N clocks, when only differences of phase-time clocks readings are available, can be carried out even supposing cross-correlation between clocks. Based on the original analysis of this problem, developed by P. Tavella and A. Premoli, and the Kuhn-Tucker theorem (1951), a new way to solve the constrained minimization problem will be introduced. We propose our particular Kuhn-Tucker equations: The already well-known constraint function and two new candidates objective functions. Advantages and inconveniences in the objective function election will be considered. Finally, our proposal will consist of solving two constrained minimization problems: the first of them to obtain an intermediate solution to be used as initial condition in the second minimization problem. Examples with some experimental data from the Real Observatorio de la Armada en San Fernando illustrate the capabilities of this proposal.

Estimating the Instabilities of N Correlated Clocks

For a GPS calibration campaign between ROA and PTB a GTR50 time and frequency transfer receiver from ROA was chosen. The operation performance of GTR50 type receivers has been validated in long term operation during the last years. The travelling GTR50 was also tested in a sequence of shutdowns and restarts to detect time jumps and malfunctions just after the restart and during the following days of operation.

A GPS calibration trip experience between ROA and PTB

This work presents a new way of understanding the geological science: the Ecological Geology. It is based on the clasical vision of the Geology as well as on some new concepts, as Geodiversity and Geoconservation. An aplication of these perspective to the Geological Heritage is also included, in a list of ten points, called Declaracion de Girona, because it is concibed in this city

J. Palacio

Papers

Improved GPS-based time link calibration involving ROA and PTB

Post-processing ROA data clocks for optimal stability in the ensemble timescale

Estimating the Instabilities of N Correlated Clocks

A GPS calibration trip experience between ROA and PTB

Geología ecológica, geodiversidad, geoconservación y Patrimonio Geológico de la Declaración de Girona