Source code for swot_simulator.error.altimeter

# Copyright (c) 2021 CNES/JPL
#
# All rights reserved. Use of this source code is governed by a
# BSD-style license that can be found in the LICENSE file.
"""
Altimeter instrument error
--------------------------
"""
from typing import Dict
import numpy as np

from .. import random_signal
from .. import settings


class Altimeter:
    """Altimeter instrument error.

    Args:
        parameters (settings.Parameters): Simulation settings
    """
    def __init__(self, parameters: settings.Parameters) -> None:
        # Store the generation parameters of the random signal.
        self.delta_al = 2 * parameters.delta_al
        self.rng = parameters.rng()
        self.len_repeat = parameters.len_repeat
        # Define the sepctrum of the nadir instrument error
        freq = np.arange(1 / 3000, 1 / self.delta_al, 1 / 3000)
        psd = 8 + 1.05 * 1e-4 * freq**(-2.2)
        psd[freq < 0.00023627939582672978] = 1e4

        # Convert spectrum in m2/cy
        self.psd = psd * 1e-4
        self.freq = freq

    def generate(self, x_al: np.array) -> Dict[str, np.ndarray]:
        """Generate altimeter instrument error.

        Args:
            x_al (numpy.ndarray): Along track distance

        Returns:
            dict: variable name and errors simulated.
        """
        # Compute random noise of 10**2 cm**2/(km/cycle)
        # Compute the correspond error on the nadir in m
        error = random_signal.gen_signal_1d(self.freq,
                                            self.psd,
                                            x_al,
                                            rng=self.rng,
                                            fmin=1 / self.len_repeat,
                                            fmax=1 / self.delta_al,
                                            alpha=10)
        return {"simulated_error_altimeter": error}