NA-SAR

NA-SAR is a North America synthetic aperture radar pretraining dataset built from NASA OPERA products. It is intended for self-supervised and masked-image pretraining of SAR foundation models.

This release is an unsplit pretraining corpus. There are no train/validation/test partitions because the dataset is not intended to define an evaluation protocol. Downstream evaluations should define their own geographically and temporally appropriate splits.

Dataset Contents

• Samples: 1,099,604
• Shards: 91 WebDataset tar shards
• Patch size: 128 x 128 pixels
• RTC views: two spatial views per sample
• Temporal RTC acquisitions: prime and secondary
• RTC channels: co-pol and cross-pol, with missing polarization zero padded
• Incidence angle: one channel per spatial view
• InSAR phase: stored as cos(phi), sin(phi)
• Coherence: one channel per spatial view
• DEM elevation: raw elevation in meters
• DEM slope: raw terrain slope in degrees

Each tensor sample contains:

Key	Shape	Description
prime_rtc_view_0	(2, 128, 128)	Prime RTC view 0, co-pol/cross-pol
secondary_rtc_view_0	(2, 128, 128)	Secondary RTC view 0, co-pol/cross-pol
prime_rtc_view_1	(2, 128, 128)	Prime RTC view 1, co-pol/cross-pol
secondary_rtc_view_1	(2, 128, 128)	Secondary RTC view 1, co-pol/cross-pol
inc_angle_view_0	(1, 128, 128)	Incidence angle for view 0
inc_angle_view_1	(1, 128, 128)	Incidence angle for view 1
ifg_view_0	(2, 128, 128)	InSAR phase for view 0 as cos/sin
coh_view_0	(1, 128, 128)	Coherence for view 0
ifg_view_1	(2, 128, 128)	InSAR phase for view 1 as cos/sin
coh_view_1	(1, 128, 128)	Coherence for view 1
dem	(1, 128, 128)	Raw DEM elevation in meters
slope_deg	(1, 128, 128)	Raw terrain slope angle in degrees

dem_relief and normalized slope are not stored in the WebDataset. They are derived at loading time from the raw dem and slope_deg arrays.

Metadata

metadata.parquet is the publishable metadata table for the sharded release. It includes OPERA provenance, patch geometry, quality score, polarization availability, and the following sharding columns:

• sample_key: sample key inside the WebDataset shard
• shard_path: relative path to the tar shard
• shard_index: integer shard id
• sample_index_in_shard: row order within that shard

The metadata is filtered to samples with quality_score > 0.53.

webdataset_summary.json records the shard count and DEM storage policy. For this release, dem_extended is "raw" and dem_arrays is ["dem", "slope_deg"].

Loading With Hugging Face Datasets

The sharded release can be streamed with the WebDataset loader:

from io import BytesIO

import numpy as np
from datasets import load_dataset

ds = load_dataset(
    "webdataset",
    data_files={"train": "data/nasar-train-*.tar"},
    split="train",
    streaming=True,
)

sample = next(iter(ds))
arrays = np.load(BytesIO(sample["npz"]))
print(arrays.files)

Loading With PyTorch

The release includes nasar_dataset.py, a lightweight PyTorch loader for the local shard layout:

from nasar_dataset import NASARWebRTCDataset, NASARWebInSARDataset

rtc_ds = NASARWebRTCDataset("/path/to/NA-SAR-HF")
insar_ds = NASARWebInSARDataset("/path/to/NA-SAR-HF", require_dem=True)

For InSAR, NASARWebInSARDataset returns SAR arrays plus DEM-derived channels:

Loader output key	Source array	Default normalization
dem_view_0/1	dem	global elevation, (-100 m, 4000 m) -> [0, 1]
dem_relief_view_0/1	dem	patch-local p5/p95 relief -> [0, 1]
slope_view_0/1	slope_deg	slope degrees, (0 deg, 45 deg) -> [0, 1]

These normalization ranges can be changed through the loader constructor.

Preprocessing Notes

RTC arrays are stored as raw linear backscatter with invalid, non-finite, and negative values set to zero. The helper loader applies the pretraining-time RTC transform by default:

x = log1p(20.0 * x)
co_pol = clip_and_rescale(co_pol, p1=0.15, p99=2.39)
cross_pol = clip_and_rescale(cross_pol, p1=0.01, p99=1.09)

The co-pol and cross-pol RTC channels use separate normalization ranges because cross-pol backscatter is substantially darker. Fully missing polarizations remain zero-padded after preprocessing.

InSAR phase is stored as cosine and sine channels instead of wrapped phase radians to avoid phase discontinuities at the wrap boundary.

DEM arrays are static for the spatial patch and shared across both orbit views. dem is raw elevation in meters. slope_deg is raw terrain slope in degrees. Derived terrain features, including global-normalized DEM, patch-local relief, and normalized slope, are intentionally computed during loading rather than stored as processed arrays.

Source and Scope

The source SAR data comes from NASA OPERA products over North America. Terrain comes from aligned DEM patches. Users should follow the applicable terms and citation guidance for OPERA and DEM source products.

Intended Use

This dataset is intended for SAR and InSAR representation learning, especially self-supervised pretraining. It is not an evaluation benchmark by itself.

Limitations

• Coverage is geographically focused on North America.
• Quality filtering removes lower-quality samples and can bias the corpus toward easier or cleaner acquisitions.
• Missing RTC polarizations are represented by zero-padded channels. The metadata includes polarization availability flags so users can distinguish true zeros from missing channels.
• DEM fields are aligned to the 128 x 128 patch grid and should not be treated as a standalone high-resolution terrain product.