SAR.py

#!/usr/bin/env python3

"""
Noise-free, clutter-free simulation of linear 1-D displacement linear FMCW radar
This sim assume cross-range displacement is small, antenna radiation pattern is hemispherical, so that a spotlight-like mode results
"""

from __future__ import annotations
from pathlib import Path
import numpy as np
from matplotlib.pyplot import show
import h5py
from argparse import ArgumentParser

#
from tincanradar.fwdmodel import fmcwtransceive
from tincanradar.plots import plotraw, rangemigration

# %% radar parameters

bm = 400e6  # Hz
tm = 0.02  # s
adcbw = 20000  # Hz
adcfs = 48000  # Hz
tfs = 550e6  # Hz #for sim only
nlfm = 0.0  # 0=perfectly linear FMCW sweep
# %% target parameters
xstart = -1.5  # m
xend = 1.5  # m
dx = 0.05  # m

x0, y0 = 0, 1.5  # m


def simsar(fn: Path | None = None):
    Ns = int(tm * adcfs)

    x = np.arange(xstart, xend, dx, dtype=float)
    y = 0  # 1-D linear displacement
    srng = np.hypot(x - x0, y - y0)
    # %% range to target --> beat frequencies
    # we do this one range at a time (like in real life), but here to conserve RAM when simulating chirp
    s = np.empty((x.size, Ns), dtype=np.complex128)
    for i, r in enumerate(srng):
        if not (i % 2):
            print(f"{i/x.size*100:.1f} %")
        s[i, :], t = fmcwtransceive(bm, tm, r, adcbw, adcfs, tfs, nlfm)

    if fn:
        fn = Path(fn).expanduser()

        with h5py.File(fn, "w") as h:
            h.create_dataset("/s", data=s, compression="gzip", shuffle=True, fletcher32=True)
            h["/t"] = t
            h["/x"] = x
            h["/y"] = y
            h["/x0"] = x0
            h["/y0"] = y0
            h["/bm"] = bm
            h["/tm"] = tm
            h["/adcbw"] = adcbw
            h["/adcfs"] = adcfs

    return s, t, x


def loadsar(fn: Path) -> tuple:
    with h5py.File(fn, "r") as h:
        s = h["/s"][:]
        t = h["/t"][:]
        x = h["/x"][:]

    return s, t, x


def procsar(s, t, x, adcfs: float, bm: float) -> None:
    plotraw(s, t, x, adcfs, bm)
    rangemigration(s, t, x, adcfs, bm)


if __name__ == "__main__":
    p = ArgumentParser()
    p.add_argument("fn", help="filename to load", nargs="?", default="first.h5")
    P = p.parse_args()

    try:
        s, t, x = loadsar(P.fn)
        procsar(s, t, x, adcfs, bm)
    except OSError:
        s, t, x = simsar(P.fn)
        procsar(s, t, x, adcfs, bm)

show()