u size imax-1,jmax and v of size imax,jmax-1; velocities on a Arakawa C grid (time invariant)

Create a sparse matrix which extract all elements of a state vector correspond to a true value in masks. masks is a tulple of boolean mask.

DIVAndrun_HFRadar(mask,h,pmn,xyi,xyobs,robs,directionobs,len,epsilon2;...)

HF Radar current analysis with DIVAnd and velocity constraints. The input parameters are:

• mask: true for sea points (false for land points) (3D-array)
• h: depth in meters (3D-array)
• pmn: inverse of the local resolution (tuple of three 3D-arrays)
• xyi: coordinates of the analysis grid (tuple of three 3D-arrays)
• xyobs: coordinates of the observations (tuple of three vectors)
• robs: radial velocity (vector)
• directionobs: angle α of the measured direction in degrees (vector) such that (see below)

\[u_{obs} \sin(α) + v_{obs} \cos(α) ≈ r_{obs}\]

• len: the correlation length (a tuple of scalars)
• epsilon2: error variance of the observation relative to the error variace of

the background estimate.

Optional input parameters

• eps2_boundary_constraint (default -1): rel. error variance of the boundary constraints
• eps2_div_constraint (default -1): rel. error variance of the divergence constraints
• eps2_Coriolis_constraint (default -1): rel. error variance of the Coriolis constraints
• f (default 0.001 s⁻¹): Coriolis parameter. For a latitude $φ$, we have on Earth :

\[\begin{aligned} Ω =& 7.2921 \; 10^{-5} rad/s \\ f =& 2 Ω \sin(φ) \end{aligned}\]

• g (default 0. m/s²): acceleration due to gravity. If g is zero, then the surface pressure is not considered; otherwise g should be set to 9.81.
• ratio (default 100): normalization factor
• lenη (default 0, 0, 24 * 60 * 60. * 10): correlation length in space and time for the surface elevation
• residual: an array of the same size as robs with the residual (output)

Convention for the direction

The bearing β is the angle at radar station (*) between North a measuring point (+) counted clockwise and the direction α is angle at measuring point between North and vector pointing to the radar station counted clockwise

                ↑ /
                |/
         ↑      +--→ current vector (u,v)
  North  |     / measurent point
         |    /
         |   /
         |  /
         |β/
         |/
         *
   radar station

Sufficiently far from the poles, we have:

\[α ≈ β + 180°\]

The $u$ zonal and $v$ meridional velocity component are related to the radial current $r$ and direction $lpha$ by:

\[\begin{aligned} u =& r \sin(α) \\ v =& r \cos(α) \\ \end{aligned}\]

\[\begin{aligned} r =& u \sin(α) + v \cos(α) \\ \tan(α) &= {u \over v} \end{aligned}\]

For HF radar data, r is positive if the velocity is pointing towards the radar site. r, u, v, direction and β consistent with the CODAR convention of the ruv files [1,2]:

A positive radial velocity is moving towards the SeaSonde, while a negative radial velocity is moving away from the SeaSonde.

[1] File Formats Used for CODAR Radial Data

[2] Technicians Information Page for SeaSondes

DIVAnd_HFRadar.cverr(
    xobs_all,yobs_all,robs_all,directionobs_all,flagcv_all,sitenames,
    lonr,latr,timerange,
    mask2d,h,
    len,lenη,eps2,
    eps2_boundary_constraint,
    eps2_div_constraint,
    eps2_Coriolis_constraint,
    g,ratio; u = [], v = [], η = [], selection = :cv)

Return the cross-validation error and potentially the analysis for a set of parameters.

Input parameters:

• xobs_all: longitude (4D array with the dimension: lon, lat, time, station)
• yobs_all: latitude (4D array with the dimension: lon, lat, time, station)
• robs_all: radial velocity (4D array with the dimension: lon, lat, time, station)
• directionobs_all: direction in degrees (4D array with the dimension: lon, lat, time, station)
• flagcv_all: true if used for validation and false otherwise (4D array with the dimension: lon, lat, time, station)
• sitenames: names of radar stations (vector of strings)
• lonr: vector of all longitude points of the grid
• latr: vector of all latitude points of the grid
• timerange: vector of all time instances (vector of DateTime)
• mask2d: 2D land-sea mask; true if sea, false is land (2D array with the dimension: lon, lat)
• h: depth (2D array with the dimension: lon, lat)
• u: the interpolated u velocity (if the parameter is not empty)
• v: the interpolated v velocity (if the parameter is not empty)
• η: the interpolated η velocity (if the parameter is not empty)
• selection: compute the analysis only of time instances with cross-validation points (:cv, default) or over all points (:all)
• Δn: time window (default 1)

See also DIVAnd_HFRadar.DIVAndrun_HFRadar for other parameters.

Note if u, v and η are provided, they should have the correct dimensions:

u = zeros(length(lonr),length(latr),length(timerange))
v = zeros(length(lonr),length(latr),length(timerange))
η = zeros(length(lonr),length(latr),length(timerange))

u size imax-1,jmax and v of size imax,jmax-1; velocities on a Arakawa C grid

Stagger from a u to a rho location in an Arakawa C grid

" Stagger from a v to a rho location in an Arakawa C grid