User-manual/General-information.md

+# Table of Contents
+
+[**1. General information**](User-Manual/General-information)
+
+- [Why LSPIV](User-Manual/General-information#question-why-lspiv)
+- [Principles of LSPIV](User-Manual/General-information#tools-principles-of-lspiv)
+- [The Open-Source Software **_Fudaa-LSPIV_**](User-Manual/General-information#computer-the-open-source-software-fudaa-lspiv)
+
+# :question: Why LSPIV
+
+Scientists studying rivers in terms of liquid flow or sediment flux often encounter a mismatch between available hydrometric measurements and their needs. These needs have evolved, in parallel with the development of numerical modeling, towards a demand for spatially distributed data, with high temporal frequency, and for diverse flow conditions. In particular, the measurement of velocity and flood discharge often remains impossible with traditional gauging techniques (current meters, ADCPs, chemical dilution), as high velocities and numerous floating debris endanger both operators and equipment. Additionally, the inherent measurement time of these techniques is often inadequate given the transient nature of flood flows. The development of 2D or even 3D modeling tools for understanding flows, in natural environments and in physical laboratory models, requires complementary measurements to water levels or discharges for validation. The spatial results in terms of velocities from these models necessitate corresponding hydrometric measurements, i.e., a velocity field. Once again, traditional velocity measurement techniques do not fully meet these needs.
+
+Hydrometry through image sequence analysis is an interesting alternative that provides access to instantaneous surface velocity measurements over areas as large as a hectare, in a non-intrusive manner. This technique is called Large Scale Particle Image Velocimetry (LSPIV). For a detailed description of the method, one can refer to the thesis by A. Hauet (2006).
+
+## :tools: Principles of LSPIV
+
+Image sequence analysis allows for the measurement of the 2D surface velocity field of a flow, provided that visible tracers, such as solid particles (vegetal debris, small floating objects, etc.), bubbles, or turbulence patterns are advected with the flow and remain recognizable from one image to another. This technique is derived from Particle Image Velocimetry (PIV) used in laboratories but is applied to large-scale objects like rivers, hence the name Large-Scale PIV (LSPIV, Fujita et al. 1998). An LSPIV measurement involves (i) recording a time-stamped sequence of flow images, (ii) geometrically correcting the images to eliminate perspective distortion effects (orthorectification), and (iii) calculating the displacement of flow tracers through statistical correlation analysis of patterns. In practice, seeding the flow with additional tracers is often unnecessary for rivers in flood: if water movement is visible in an image sequence, it is generally possible to extract velocities from it. This results in a "quasi-instantaneous" 2D field (at the sampling frequency of the image pairs, limited by the camera’s acquisition frequency and the amplitude of pattern displacements). Knowing the bathymetry of a cross-section and assuming a vertical velocity distribution model, one can estimate discharge from the LSPIV velocity field.
+
+LSPIV has been used to estimate river discharges at very different scales, from low flows to large floods (see, for example, Creutin et al. 2003, Hauet et al. 2008, or Jodeau et al. 2008), as well as to improve rating curves under normal hydraulic conditions (Le Coz et al. 2010 or Dramais et al. 2011). LSPIV has also been applied to flood videos shared by the public on the internet (Le Boursicaud et al. 2016, Le Coz et al. 2016). A review of LSPIV applications for river discharge estimation was provided by Muste et al. (2008). LSPIV has also been used for the study of complex flow dynamics (Le Coz et al. 2010b, Hauet et al. 2009) as well as for debris flows (Theule et al. 2018) and mobile bed physical models (Piton et al., 2018). LSPIV has also proven to be an effective tool for studying runoff flows on slopes (Nord et al. 2009, Legout et al. 2012), where intrusive instruments cannot be used due to the very low water depths considered (millimeters).
+
+# :computer: The Open-Source Software **_Fudaa-LSPIV_**
+
+**_Fudaa-LSPIV_** is software designed to process flow image sequences to calculate surface velocity fields and discharges across cross-sections. The method is based on the LSPIV (Large-Scale Particle Image Velocimetry) technique, with the following main steps:
+
+- _Images_: import an image sequence or sampled images from a video sequence
+- _Orthorectification_: correct images for perspective distortion and assign a metric scale to pixels
+- _LSPIV Analysis_: calculate surface velocities based on statistical analysis of tracer movement
+- _Post-processing_: apply filters to velocity results, calculate the time average, calculate streamlines
+- _Discharge_: calculate discharge across a bathymetric transect using a velocity correction coefficient
+
+The open-source software (GPL license) **_Fudaa-LSPIV_** is a Java interface that calls Fortran and C++ executables. The development of **_Fudaa-LSPIV_** has been carried out by DeltaCAD since August 2010, with funding and under the direction of EDF and INRAE. This development is part of the Fudaa open-source software project for hydraulic applications. Supported languages are French and English, and the software can be used on Windows or Linux operating systems. The distribution terms are those of free GPL licenses, and the software is the intellectual property of EDF and INRAE.
+
+The calculation codes common to Fudaa-LSPIV and the mobile application FlowPic are developed by INRAE and EDF. They are open-source (GPL license) and available here: https://gitlab.irstea.fr/image_velocimetry/velocimetry_solver
+
+#  
+-> [**Next Section: 2. Getting Started with Fudaa-LSPIV**](User-Manual/getting-started-with-fudaa-lspiv)