This repository contains routines that adapt litebird_sim to LSPE-SWIPE.
It sould contain:
- Modules which takes care of the scanning strategy for a Balloon
- A number of modules that can ingest systematic effects in the timelines
Set up the enviroment (if necessary)
# Create a conda environment
conda create -n swipe_env python=3.8
# Activate the environment
conda activate swipe_env
Obviously a similar structure works also for virtualenv
Install the package
git clone https://github.com/paganol/swipe_modules.git
cd swipe_modules
pip install .
It can be installed in editable mode with pip install -e .
Download the IMO from the github repository and run
python -m litebird_sim.install_imo
Select option 3 and enter the directory swipe_imo/IMO insert a descriptive name, something like SWIPE_IMO, and save with s
from swipe_modules import SwipeSpinScanningStrategy
import litebird_sim as lbs
import healpy as hp
import astropy
# Initialize the simulation
sim = lbs.Simulation(
start_time=astropy.time.Time("2026-09-01T16:00"),
duration_s=36*3600, # 36 hrs of mission
description="SWIPE simulation",
random_seed=12345,
)
# Scanning strategy
# delta_time_s is important, it sets the resolution of the computed pointing
# (then pointing gets interpolated at the sampling frequency)
# litebird_sim's default is 60sec, for SWIPE a more frequent sampling, 1sec is reasonably good
scanning = SwipeSpinScanningStrategy()
sim.set_scanning_strategy(scanning,delta_time_s=1)
# Initialize the instrument, this might be done using the IMo
# Here spin_boresight_angle_rad is practically ``pi/2 - elevation``
instr = lbs.InstrumentInfo(
name="SWIPE",
spin_boresight_angle_rad=np.deg2rad(90.0-51.5),
)
det = lbs.DetectorInfo(name="foo", sampling_rate_hz=100)
# Observation and pointing
sim.set_instrument(instr)
obs, = sim.create_observations(detectors=[det])
sim.prepare_pointings()
sim.precompute_pointings()
# Plot the scan
nside = 128
npix = hp.nside2npix(nside)
h = np.zeros(npix)
for idet in [0]:
pixidx = hp.ang2pix(nside, obs.pointing_matrix[idet, :, 0], obs.pointing_matrix[idet, :, 1])
pixel_occurrences = np.bincount(pixidx)
h[0:len(pixel_occurrences)] += pixel_occurrences
hp.mollview(h)
The relevant class for the spin scanning strategy is SwipeSpinScanningStrategy.
It takes the following parameters:
- `site_latitude_deg`: latitude of the launching site in deg
- `site_longitude_deg`: longitude of the launching site in deg
- `longitude_speed_deg_per_sec`: longitude speed in deg/sec
- `spin_rate_rmp`: the number of rotations per minute (RPM) around
the spin axis
- `start_time`: an ``astropy.time.Time`` object representing the
start of the observation. It's currently unused, but it is meant
to represent the time when the rotation starts (i.e., the angle
ωt is zero).
- `balloon_latitude_deg`: latitude of a tabulated trajectory
- `balloon_longitude_deg`: longitude of a tabulated trajectory
- `balloon_time`: list of astropy.time.Time
For a constant elevation scan in azimuth the class to use is SwipeRasterScanningStrategy.
It takes the following parameters:
- `site_latitude_deg`: latitude of the launching site in deg
- `site_longitude_deg`: longitude of the launching site in deg
- `longitude_speed_deg_per_sec`: longitude speed in deg/sec
- `azimuth_start_deg`: start azimuth for constant elevation scan
- `azimuth_amplitude_deg`: amplitude in azimuth for constant elevation scan
- `azimuth_scan_speed_deg_per_s`: scan speed in azimuth
- `start_time`: an ``astropy.time.Time`` object representing the
start of the observation. It's currently unused, but it is meant
to represent the time when the scan starts.
- `balloon_latitude_deg`: latitude of a tabulated trajectory
- `balloon_longitude_deg`: longitude of a tabulated trajectory
- `balloon_time`: list of astropy.time.Time
In both cases if balloon_latitude_deg, balloon_longitude_deg and balloon_time
are provided a tabulated trajectory will be used.