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Native weather-satellite decoders (app/radio/sat)

A clean-room replacement for SatDump's common decode chains, built from published standards (CCSDS 131.0-B, the NOAA KLM User's Guide, the LRIT/HRIT specs). No SatDump source or binary is used as a source or oracle. SatDump is still driven as an external program for the exotic instruments, map projections and Inmarsat that these don't cover (see satdecode.py).

The stack

        IQ (RTL/Lime/Airspy)  or  FM audio (the 705)
                 │
   qpsk_rx ──────┤  AGC · RRC · Gardner timing · Costas (QPSK & BPSK)
                 │
   ccsds ────────┤  r=1/2 K=7 Viterbi · ASM 0x1ACFFC1D · TM derandomiser
                 │  · RS(255,223) dual basis · CADU→VCDU  (single & streaming)
                 │
  extract_packets┤  VCDU M_PDU → CCSDS Space Packets (spanning frames)
                 │
   per-mode ─────┴  APT / LRPT (Meteor JPEG) / xRIT / HRPT / AHRPT (AVHRR)
Module Role
viterbi.py CCSDS r=1/2 K=7 conv code + vectorised soft Viterbi (numpy ACS)
rs.py RS(255,223), CCSDS field 0x187, fcr=112, generated dual-basis transform
ccsds.py ASM sync, TM PN (spec-exact), CADU chain, decode_stream (all CADUs)
qpsk_rx.py real-IQ QPSK and BPSK receivers + impaired-capture generators
apt.py NOAA APT — 2400 Hz AM subcarrier → line sync → image (FM audio, no SDR)
meteor_jpeg.py Meteor MSU-MR image codec (JPEG-Huffman + DCT + Meteor quant)
lrpt.py Meteor LRPT — QPSK → CCSDS → packets → image; single + full-pass
xrit.py LRIT/HRIT file layer (GOES/Meteosat); uncompressed + JPEG (Pillow)
hrpt.py NOAA HRPT/AVHRR — Manchester, 10-bit words, frame sync, de-interleave
ahrpt.py MetOp/FengYun AHRPT — raw AVHRR over the CCSDS core
avhrr.py image products — stretch, grayscale, RGB composite, montage
decode_file.py offline CLI + the app's native SatDecoder backend

Offline CLI

python -m app.radio.sat.decode_file apt   noaa.wav                    -o img.png
python -m app.radio.sat.decode_file lrpt  meteor.iq  --fs 140000      -o img.png
python -m app.radio.sat.decode_file hrpt  hrpt.iq    --fs 2662000     -o avhrr.png
python -m app.radio.sat.decode_file ahrpt metop.iq   --fs 2000000 --product rgb

In the app

  • 🛰 per recording → sat_decode_file → SatDecoder.decode_recording. A WAV decodes as APT; an IQ recording decodes with the mode from its JSON sidecar.
  • 📡 IQ REC → record_iq captures SDR IQ to rec-<ts>-iq.iq + a sidecar, so the pass lands in the list and its 🛰 button decodes it natively.
  • 🛰 LIVE → sat_stream → NativeSatStreamer decodes off the SDR in real time, the image building up in the SATS pane during the pass.

What is validated, and what needs a real signal

Validated (self-consistent + spec-transcribed, 50 tests): the FEC/framing/ codecs, the real-IQ receivers, the in-app decode/dispatch, and the streaming accumulation logic (fed IQ chunks through an injectable source). Every mode round-trips through impaired synthetic captures (carrier offset, symbol-timing offset, phase, noise); the CCSDS PN matches the spec vector; RS corrects 16 errors; LRPT/HRPT/AHRPT recover images from raw IQ.

Hardware-gated (code complete, needs a real SDR/signal to run): - The IQ recording and live streaming capture paths — the decode side is tested; the SDR read loop needs a device. - The exact NOAA HRPT minor-frame sync word and a real-signal interop pass. - AVHRR radiometric calibration (albedo / brightness temperature) — the products here are display-grade (contrast-stretched), not calibrated.