updates to swapi ialirt fitting algorithm

imap_processing/ialirt/constants.py

@@ -39,6 +39,13 @@ class IalirtSwapiConstants:
     speed_ew = 0.5 * fwhm_width  # speed width of energy passband
     e_charge = 1.602176634e-19  # electronic charge, [C]
     speed_coeff = np.sqrt(2 * e_charge / prot_mass) / 1e3
+
+    # temporary correction factor based on WIND data available
+    # overlapping with the first ~month of SWAPI data.
+    # to be replaced once SWAPI's L3 processing pipeline is finalized
+    # this will increase the model count by a factor of e^1,
+    # changing the output density by a factor of e^-1.
+    temporary_density_factor = np.exp(1)
 
 
 class StationProperties(NamedTuple):

imap_processing/ialirt/l0/process_swapi.py

@@ -2,6 +2,7 @@
 
 import logging
 from decimal import Decimal
+from math import isfinite
 
 import numpy as np
 import pandas as pd
@@ -22,6 +23,7 @@
 logger = logging.getLogger(__name__)
 
 NUM_IALIRT_ENERGY_STEPS = 63
+FILLVAL_FLOAT32 = -1.0e31
 
 
 def count_rate(
@@ -57,6 +59,9 @@ def count_rate(
     speed = speed * 1000  # convert km/s to m/s
     density = density * 1e6  # convert 1/cm**3 to 1/m**3
 
+    # see comment on Consts.temporary_density_factor
+    density = density * Consts.temporary_density_factor
+
     return (
         (density * Consts.eff_area * (beta / np.pi) ** (3 / 2))
         * (np.exp(-beta * (center_speed**2 + speed**2 - 2 * center_speed * speed)))
@@ -104,15 +109,42 @@ def optimize_pseudo_parameters(
             60000 * (initial_speed_guess / 400) ** 2,
         ]
     )
-    sol = curve_fit(
-        f=count_rate,
-        xdata=energy_passbands.take(range(max_index - 3, max_index + 3), mode="clip"),
-        ydata=count_rates.take(range(max_index - 3, max_index + 3), mode="clip"),
-        sigma=count_rate_error.take(range(max_index - 3, max_index + 3), mode="clip"),
-        p0=initial_param_guess,
-    )
-
-    return sol[0]
+
+    sol = None
+
+    try:
+        five_point_range = range(max_index - 2, max_index + 2 + 1)
+        xdata = energy_passbands.take(five_point_range, mode="clip")
+        ydata = count_rates.take(five_point_range, mode="clip")
+        sigma = count_rate_error.take(five_point_range, mode="clip")
+        curve_fit_output = curve_fit(
+            f=count_rate,
+            xdata=xdata,
+            ydata=ydata,
+            sigma=sigma,
+            p0=initial_param_guess,
+        )
+
+        # if covariance matrix is not finite, scipy failed to converge to a solution and could just be reporting the initial guess
+        covariance_matrix_is_finite = np.all(np.isfinite(curve_fit_output[1]))
+
+        # fit has failed if R^2 < 0.7
+        yfit = count_rate(xdata, *curve_fit_output[0])
+        R2 = 1 - np.sum((ydata - yfit) ** 2) / np.sum((ydata - ydata.mean()) ** 2)
+        R2_is_acceptable = R2 >= 0.7
+
+        if covariance_matrix_is_finite and R2_is_acceptable:
+            sol = curve_fit_output[0]
+    except RuntimeError as runtime_error:
+        logger.error(f"curve_fit failed", runtime_error)
+        sol = None
+
+    # report speed only if fit fails            
+    if sol is None:
+        sol = initial_param_guess.copy()
+        sol[1:] = FILLVAL_FLOAT32 
+
+    return sol
 
 
 def geometric_mean(
@@ -237,8 +269,9 @@ def process_swapi_ialirt(
         grouped_subset = grouped_dataset.sel(epoch=grouped_dataset.group == group)
 
         raw_coin_count = process_sweep_data(grouped_subset, "swapi_coin_cnt")
-        # I-ALiRT packets are 16 times less than the regular science packets.
-        raw_coin_count = raw_coin_count * 16
+        # I-ALiRT packets have counts compressed by a factor of 16.
+        # Add 8 to avoid having counts truncated to 0 and to avoid counts being systematically too low
+        raw_coin_count = raw_coin_count * 16 + 8
         # Subset to only the relevant I-ALiRT energy steps
         raw_coin_count = raw_coin_count[:, :NUM_IALIRT_ENERGY_STEPS]
         raw_coin_rate = raw_coin_count / SWAPI_LIVETIME

imap_processing/tests/ialirt/unit/test_process_swapi.py

@@ -7,6 +7,8 @@
 
 from imap_processing import imap_module_directory
 from imap_processing.ialirt.l0.process_swapi import (
+    FILLVAL_FLOAT32,
+    Consts,
     count_rate,
     geometric_mean,
     optimize_pseudo_parameters,
@@ -184,8 +186,8 @@ def test_count_rate():
     """Use random realistic values to test for expected output of count_rate()."""
 
     actual_result = count_rate(1370, *[550, 5.27, 1e5])
-    expected_result = 3073.023325893161
-    assert actual_result == expected_result, (
+    expected_result = 3073.023325893161 * Consts.temporary_density_factor
+    assert np.isclose(actual_result, expected_result), (
         f"The actual result of count_rate()"
         f" {actual_result} does not "
         f"match the expected result "
@@ -202,24 +204,24 @@ def test_optimize_parameters():
             "file_name": "ialirt_test_data_u_sw_550_n_sw_5_T_sw_100000_v2.csv",
             "expected_values": {  # expected output and acceptable tolerance
                 "pseudo_speed": (550, 0.01),
-                "pseudo_density": (5, 0.14),
-                "pseudo_temperature": (1e5, 0.2),
+                "pseudo_density": (5 / Consts.temporary_density_factor, 0.14),
+                "pseudo_temperature": (1e5, 0.25),
             },
         },
         "test_set_2": {
             "file_name": "ialirt_test_data_u_sw_650_n_sw_3.0_T_sw_120000_v2.csv",
             "expected_values": {  # expected output and acceptable tolerance
                 "pseudo_speed": (650, 0.01),
-                "pseudo_density": (3, 0.3),
+                "pseudo_density": (3 / Consts.temporary_density_factor, 0.3),
                 "pseudo_temperature": (1.2e5, 0.28),
             },
         },
         "test_set_3": {
             "file_name": "ialirt_test_data_u_sw_400_n_sw_6.0_T_sw_80000_v2.csv",
             "expected_values": {  # expected output and acceptable tolerance
                 "pseudo_speed": (400, 0.01),
-                "pseudo_density": (6, 0.39),
-                "pseudo_temperature": (8e4, 0.15),
+                "pseudo_density": (6 / Consts.temporary_density_factor, 0.39),
+                "pseudo_temperature": (8e4, 0.2),
             },
         },
     }
@@ -259,6 +261,93 @@ def test_optimize_parameters():
             )
 
 
+def test_optimize_parameters_exception_handling():
+    """Test that the optimize_pseudo_parameters() function reports speed only when given data that causes curve_fit to fail."""
+
+    expected_speed = 557.279273 # peak passband speed
+    file_name = "ialirt_test_data_u_sw_550_n_sw_5_T_sw_100000_v2.csv"
+
+    calibration_test_file = pd.read_csv(
+        f"{imap_module_directory}/tests/ialirt/data/l0/swapi_ialirt_energy_steps.csv"
+    )
+    energy_passbands = calibration_test_file["Energy"][0:63].to_numpy().astype(float)
+
+    energy_data = pd.read_csv(f"{imap_module_directory}/tests/ialirt/data/l0/{file_name}")
+    count_rates = energy_data["Count Rates [Hz]"].to_numpy()
+    count_rates[0] = 0.0
+    count_rates = np.tile(count_rates, (2, 1))
+    count_rates_errors = energy_data["Count Rates Error [Hz]"].to_numpy()
+
+    """
+    code to select the random seed:
+    for i in range(100):
+    np.random.seed(i)
+    result = optimize_pseudo_parameters(count_rates * np.abs(np.random.standard_normal(size=count_rates.shape)), count_rates_errors, energy_passbands)
+    if np.isclose(result['pseudo_speed'][0], expected_speed, rtol=1e-6) and np.isnan(result['pseudo_density'][0]):
+        print(i)
+    """
+    np.random.seed(14)
+    speed, density, temperature = optimize_pseudo_parameters(count_rates * np.abs(np.random.standard_normal(size=count_rates.shape)), count_rates_errors, energy_passbands)
+
+    np.testing.assert_allclose(speed, expected_speed, rtol=1e-6)
+    np.testing.assert_allclose(density, FILLVAL_FLOAT32)
+    np.testing.assert_allclose(temperature, FILLVAL_FLOAT32)
+
+
+def test_optimize_parameters_bad_fit_handling():
+    """Test that the optimize_pseudo_parameters() function reports speed only when the fit is too poor."""
+
+    file_name = "ialirt_test_data_u_sw_550_n_sw_5_T_sw_100000_v2.csv"
+
+    calibration_test_file = pd.read_csv(
+        f"{imap_module_directory}/tests/ialirt/data/l0/swapi_ialirt_energy_steps.csv"
+    )
+    energy_passbands = calibration_test_file["Energy"][0:63].to_numpy().astype(float)
+
+    energy_data = pd.read_csv(f"{imap_module_directory}/tests/ialirt/data/l0/{file_name}")
+    count_rates = energy_data["Count Rates [Hz]"].to_numpy()
+    count_rates[0] = 0.0
+    count_rates_errors = energy_data["Count Rates Error [Hz]"].to_numpy()
+
+    # add high-amplitude randomness to the count rates to make the fit poor
+    np.random.seed(0)
+    count_rates = count_rates + np.abs(np.random.standard_normal(size=count_rates.shape) * count_rates.max())
+
+    speed, density, temperature = optimize_pseudo_parameters(count_rates, count_rates_errors, energy_passbands)
+
+    expected_speed = np.sqrt(energy_passbands[count_rates.argmax(axis=-1)]) * Consts.speed_coeff
+
+    np.testing.assert_allclose(speed, expected_speed, rtol=1e-6)
+    np.testing.assert_allclose(density, FILLVAL_FLOAT32)
+    np.testing.assert_allclose(temperature, FILLVAL_FLOAT32)
+
+
+def test_optimize_parameters_bad_covariance_handling():
+    """Test that the optimize_pseudo_parameters() function reports speed only when output covariance is nonsensical."""
+
+    file_name = "ialirt_test_data_u_sw_550_n_sw_5_T_sw_100000_v2.csv"
+
+    calibration_test_file = pd.read_csv(
+        f"{imap_module_directory}/tests/ialirt/data/l0/swapi_ialirt_energy_steps.csv"
+    )
+    energy_passbands = calibration_test_file["Energy"][0:63].to_numpy().astype(float)
+
+    energy_data = pd.read_csv(f"{imap_module_directory}/tests/ialirt/data/l0/{file_name}")
+    count_rates = energy_data["Count Rates [Hz]"].to_numpy()
+    count_rates[0] = 0.0
+    count_rates_errors = energy_data["Count Rates Error [Hz]"].to_numpy()
+
+    # setting errors to 0 results in infinite covariance
+    count_rates_errors *= 0
+
+    speed, density, temperature = optimize_pseudo_parameters(count_rates, count_rates_errors, energy_passbands)
+
+    expected_speed = np.sqrt(energy_passbands[count_rates.argmax(axis=-1)]) * Consts.speed_coeff
+
+    np.testing.assert_allclose(speed, expected_speed, rtol=1e-6)
+    np.testing.assert_allclose(density, FILLVAL_FLOAT32)
+    np.testing.assert_allclose(temperature, FILLVAL_FLOAT32)
+
 def test_geometric_mean():
     """Test geometric_mean function."""