examples/plot_sampling_reqs.jl

+include(joinpath("..", "src", "sampling_requirements.jl"))
+include(joinpath("..", "src", "plot_basics.jl"))
+
+function plot_geom_sampling_reqs(z, D1, Dn=D1; λ=1.55e-6, Nd=251, bw=1 / 1e-2, relax=false)
+
+    # at least 10 samples within the ROIs D1 and Dn
+    dx1 = range(D1 / 100, D1 / 10, Nd)
+    dxn = range(Dn / 100, Dn / 10, Nd) 
+    dxnt = transpose(dxn)
+
+    # compare my notes on the relaxation of the sampling requirement (2) for a source with bandwidth < 1/dx1, e.g., bw ~ 1/w0 = 1 / 1e-2
+    c = if relax
+        @. inv(bw * dx1)
+    else
+        1
+    end
+
+    # second requirement
+    Nmin = @. D1 / 2dx1 + Dn / dxnt + λ * z / (2 * dx1 * dxnt * c)
+    # first requirement
+    dxnmax = @. (λ * z - Dn * dx1) / D1
+
+    # 2D representation of second requirement
+    z = log2.(Nmin)
+    # enforce first requirement
+    @. z[dxnt > dxnmax] = Inf
+
+    plt = plot.contour(x=dx1 * 1e3, y=dxn * 1e3, z=z, contours=Config(showlabels=true, labelfont=Config(color="white"), size=2), colorbar=Config(title=Config(text="log<sub>2</sub>(N<sub>min</sub>)"))) # predefined levels not working - for whatever reason -.-
+
+    plt.layout.xaxis.title = "dx1 / mm"
+    plt.layout.yaxis.title = "dxn / mm"
+    # plt.layout.yaxis.scaleanchor = "x"
+    plt.layout.yaxis.autorange = true
+    plt.layout.title = "Sampling Requirements 1 & 2"
+
+    display(plt)
+    return
+end
\ No newline at end of file

examples/repeated_wave_propagation.jl

@@ -29,7 +29,7 @@ function repeated_wave_propagation(utx::AbstractArray{Complex{T}}, midx, domain:
     zr = 2π / λ * w0^2 / 2
     wz = w0 * sqrt(1 + domain.Dz^2 / zr^2)
     # effective transmit aperture
-    D1 = 2w0
+    D1 = 4w0
     # effective receive aperture, super-Gaussian window function reduces effective domain size to 2*0.47*Dxy (1/e, see split-step-method.jl)
     # D2 = min(2domain.rA, 0.94domain.Dx, 0.94domain.Dy, 2wz)
     D2 = 4wz

src/sampling_requirements.jl

@@ -35,6 +35,7 @@ function check_geometry_sampling(z::Number, N, dx1, D1, dx2=dx1, D2=D1/2; λ=1.5
 
     # determine the necessary spatial extent of the observation-plane grid, compare Schmidt 2010 (7.20)
     Nmin = D1 / 2dx1 + D2 / 2dx2 + λ * z / (2 * dx1 * dx2)
+    # note that this value is computed under the assumption of a source bandwidth 1/dx1! If this bandwidth is actually lower, this requirement can be relaxed.
 
     req2 = N ≥ Nmin
     debug && (@info "Criterion (2) (N): N ≥ $Nmin")