odsl-swot-download queries NASA Earthdata (CMR) for SWOT L2 LR SSH granules, writes per-cycle manifests, and downloads whatever is missing. It is fully idempotent: files already on disk are skipped, so re-running it simply tops up the archive with newly released passes.

What you'll learn

  • Checking what is already on /spray before downloading anything.
  • Setting up NASA Earthdata credentials (~/.netrc).
  • Downloading a cycle range of the Expert product.
  • Grabbing the link for a single granule with odsl-swot-granule-link.

Prerequisites: tutorial 1 (environment activated).

1. First, check what's already there

On the lab server most of the archive is already maintained. Before downloading, look:

ls /spray/swot/versionD                          # which cycles exist
ls /spray/swot/versionD/cycle_020 | wc -l        # how many passes in cycle 20

A complete science-phase cycle has up to 584 pass files (some are always missing — not every pass produces a granule). The per-cycle manifests in the repo's database/ folder record what the archive should contain:

ls database/expert_cycle_020*

database/expert_cycle_020.csv                 # selected file per pass
database/expert_cycle_020_download_links.csv  # every link CMR returned

If the cycles you need are present, skip straight to tutorial 3.

2. Earthdata credentials (~/.netrc)

Downloading (not reading!) requires a free NASA Earthdata account (https://urs.earthdata.nasa.gov). Store the credentials in ~/.netrc:

machine urs.earthdata.nasa.gov login <username> password <password>

chmod 600 ~/.netrc

All ODSL downloaders authenticate through this file via earthaccess — you never type a password into a script.

3. Download a cycle range

Download the Expert product for science cycles 20–30 into the default /spray/swot/versionD root:

odsl-swot-download --cycle-start 20 --cycle-end 30 --product-type Expert

For each cycle the tool:

  1. queries CMR for all granule links and writes database/expert_cycle_###_download_links.csv;
  2. picks the best available version of each pass (newer processing versions win) and writes database/expert_cycle_###.csv;
  3. downloads the files that are missing from cycle_###/ under the data root.

Existing per-cycle link lists are reused, except the last cycle in the range, which is always re-queried — that is how an ongoing cycle picks up newly released passes. Progress is appended to swot/swot_downloader.log.

--product-type accepts Basic, Expert, Unsmoothed, or WindWave (case-insensitive); Expert is the default.

Downloading to your own directory

Off the lab server (or for a private copy), redirect both the data root and the manifest directory:

odsl-swot-download --cycle-start 1 --cycle-end 5 \
    --data-root /scratch/$USER/swot \
    --database-dir /scratch/$USER/swot/database

Paranoid mode

Two optional integrity flags:

odsl-swot-download --cycle-start 20 --cycle-end 30 \
    --validate-urls        # HEAD-check each URL before downloading
    --verify-downloads     # verify each fresh file against remote metadata

Both slow things down; use them when a previous run was interrupted or you suspect truncated files.

4. One granule at a time

When you just want a link — to wget on another machine, to share, or to check what version is current — use odsl-swot-granule-link with a cycle and pass number:

odsl-swot-granule-link 20 13

https://archive.podaac.earthdata.nasa.gov/.../SWOT_L2_LR_SSH_Expert_020_013_..._PGC0_01.nc

It prints the preferred link (highest processing version). --all prints every matching link instead, and --product-prefix switches product (default SWOT_L2_LR_SSH_Expert):

odsl-swot-granule-link 20 13 --all
odsl-swot-granule-link 20 13 --product-prefix SWOT_L2_LR_SSH_Unsmoothed

Troubleshooting

  • Authentication errors — check ~/.netrc spelling (machine urs.earthdata.nasa.gov), permissions (chmod 600), and that your Earthdata password contains no characters your shell mangled when you created the file.
  • A cycle returns zero links — the cycle probably hasn't been flown or released yet (science cycles appear roughly every 21 days), or you asked for a cal/val-range cycle number that doesn't exist for this product. Remember the cycle-numbering gotcha.
  • A run was interrupted — just re-run the same command; existing files are skipped. Add --verify-downloads if you suspect a partial file.

Next: Tutorial 3 — Finding passes over your region.