diff --git a/phenology_timesat.py b/phenology_timesat.py
new file mode 100644
index 0000000..2ce2a85
--- /dev/null
+++ b/phenology_timesat.py
@@ -0,0 +1,738 @@
+"""
+PhenoCam GCC: green-up and green-down (50 % of seasonal amplitude) via TIMESAT.
+
+Reads ``data/.../raw/phenocam/phenocam_gcc.json`` (or any path) and uses the
+``timesat`` package (``timesat.tsfprocess``) with the same seasonal-threshold
+meaning as the TIMESAT GUI: *startmethod* 1, *p_startcutoff* (0.5, 0.5) = 50 % of
+the **per-season** amplitude above the local base. See the TIMESAT manual,
+section 4.3 and row 37–38 (season start method = seasonal amplitude).
+
+**License:** the ``timesat`` PyPI wheel is under the TIMESAT Research License
+(non-commercial research; see package metadata on PyPI).
+
+PhenoCam time series: single-year acquisition writes
+  ``phenocam_gcc.json`` (and ``phenocam_gcc.csv``). The three-year series used
+  for TIMESAT is stored separately as ``phenocam_gcc_3y.json`` in the same
+  folder (created on first use from the one-day summary API, then reused).
+
+Importable: ``write_phenocam_phenology_for_site`` is called from ``run.py``;
+the CLI entry point remains optional for ad-hoc runs.
+
+**Saving results:** use ``-o path.json`` or ``--sidecar`` to write a JSON file
+(see ``--help``). Sidecar mode writes ``phenocam_phenology.json`` (two dates
+only) next to ``phenocam_gcc.json``.
+
+``run_pipeline`` in ``run.py`` writes the same ``phenocam_phenology.json`` by
+default when ``timesat`` is installed. GCC for TIMESAT uses ``phenocam_gcc_3y.json``
+if present, otherwise the PhenoCam API for that site (listed in
+``data/sites.geojson``; not a site list from the API). One-year
+``phenocam_gcc.json`` on disk can still fill gaps when merged.
+
+Use ``python phenology_timesat.py --all`` to batch every
+``(sitename, season)`` from ``data/sites.geojson`` (``properties.sitename`` and
+``properties.seasons``).
+"""
+
+from __future__ import annotations
+
+import argparse
+import csv
+import json
+import sys
+from datetime import datetime, timedelta
+from pathlib import Path
+
+import numpy as np
+import requests
+
+PHENOCAM_API = "https://phenocam.nau.edu/api"
+
+try:
+    import timesat as _timesat
+except ImportError:
+    _timesat = None
+
+NODATA = -9999.0
+
+
+def load_phenocam_gcc(path: Path) -> dict[str, float]:
+    """Return map YYYY-MM-DD -> greenness index from PhenoCam JSON list."""
+    with open(path) as f:
+        rows = json.load(f)
+    out: dict[str, float] = {}
+    for row in rows:
+        d = str(row.get("date", ""))[:10]
+        v = row.get("greenness_index")
+        if d and v is not None and np.isfinite(v):
+            out[d] = float(v)
+    return out
+
+
+def _gcc_from_summary_row(row: dict, use_mean_fallback: bool) -> float | None:
+    """Extract daily GCC from a one-day summary row (same rules as acquisition)."""
+    if not use_mean_fallback:
+        oflag = row.get("outlierflag_gcc_90")
+        if oflag is not None and str(oflag).strip() in ("1", "1.0"):
+            return None
+
+    raw = row.get("gcc_mean" if use_mean_fallback else "gcc_90")
+    if raw is None:
+        return None
+    text = str(raw).strip()
+    if not text or text.upper() == "NA":
+        return None
+    try:
+        val = float(text)
+    except ValueError:
+        return None
+    if val <= -9998.0:
+        return None
+    return val
+
+
+def _phenocam_one_day_summary_csv_url(site_name: str) -> str | None:
+    """Return URL of the one-day summary CSV for *site_name*, or None on failure."""
+    try:
+        url = f"{PHENOCAM_API}/roilists/"
+        params: dict | None = {"site": site_name}
+        rois: list[dict] = []
+        while url:
+            r = requests.get(url, params=params, timeout=30)
+            r.raise_for_status()
+            data = r.json()
+            rois.extend(
+                [roi for roi in data.get("results", []) if roi["site"] == site_name]
+            )
+            url = data.get("next")
+            params = None
+            if rois:
+                break
+        if not rois:
+            return None
+        return rois[0].get("one_day_summary") or None
+    except requests.RequestException:
+        return None
+
+
+def _parse_phenocam_gcc_from_csv_text(
+    text: str, start_date: str, end_date: str
+) -> dict[str, float]:
+    """Map YYYY-MM-DD -> gcc for rows in [start_date, end_date] inclusive."""
+    start_dt = datetime.strptime(start_date, "%Y-%m-%d")
+    end_dt = datetime.strptime(end_date, "%Y-%m-%d")
+    lines = [line for line in text.split("\n") if line and not line.startswith("#")]
+    reader = csv.DictReader(lines)
+    fieldnames = reader.fieldnames or ()
+    use_mean_fallback = "gcc_90" not in fieldnames
+    out: dict[str, float] = {}
+    for row in reader:
+        try:
+            date_str = row.get("date")
+            if not date_str:
+                continue
+            date = datetime.strptime(date_str, "%Y-%m-%d")
+            if not (start_dt <= date <= end_dt):
+                continue
+            gcc = _gcc_from_summary_row(row, use_mean_fallback)
+            if gcc is not None:
+                out[date.date().isoformat()] = gcc
+        except (ValueError, KeyError):
+            continue
+    return out
+
+
+def save_phenocam_gcc_json(path: Path, by_date: dict[str, float]) -> None:
+    """Write the same list-of-objects format as :func:`acquisition_phenocam` GCC JSON."""
+    rows = [
+        {"date": d, "greenness_index": v}
+        for d, v in sorted(by_date.items(), key=lambda x: x[0])
+    ]
+    path.parent.mkdir(parents=True, exist_ok=True)
+    with open(path, "w", encoding="utf-8") as f:
+        json.dump(rows, f, indent=2)
+        f.write("\n")
+
+
+def fetch_phenocam_gcc_three_years_separately(
+    site_name: str, season: int
+) -> dict[str, float]:
+    """
+    Download PhenoCam one-day summary GCC for three **calendar** years
+    (``season-1`` … ``season+1``), independently of :mod:`acquisition_phenocam`.
+
+    Uses one HTTP GET of the full summary CSV, then **three** per-year
+    extractions (same logic as the acquisition CSV filter, three date windows).
+    """
+    out: dict[str, float] = {}
+    csv_url = _phenocam_one_day_summary_csv_url(site_name)
+    if not csv_url:
+        print(
+            f"[PhenoCam phenology] No PhenoCam one-day summary URL for site {site_name!r}"
+        )
+        return out
+    try:
+        csv_r = requests.get(csv_url, timeout=30)
+        csv_r.raise_for_status()
+    except requests.RequestException as e:
+        print(f"[PhenoCam phenology] API CSV fetch failed: {e}")
+        return out
+    text = csv_r.text
+    for y in (season - 1, season, season + 1):
+        part = _parse_phenocam_gcc_from_csv_text(text, f"{y}-01-01", f"{y}-12-31")
+        out.update(part)
+    return out
+
+
+def load_or_fetch_phenocam_gcc_3y(
+    site_name: str, season: int, gcc_3y_path: Path
+) -> dict[str, float]:
+    """
+    Use ``phenocam_gcc_3y.json`` on disk if it exists and parses; else fetch
+    three years from the PhenoCam one-day summary for *site_name* and save to
+    *gcc_3y_path*.
+    """
+    if gcc_3y_path.is_file():
+        try:
+            cached = load_phenocam_gcc(gcc_3y_path)
+        except (OSError, json.JSONDecodeError):
+            cached = {}
+        if cached:
+            print(f"[PhenoCam phenology] Using {gcc_3y_path} ({len(cached)} values)")
+            return cached
+    out = fetch_phenocam_gcc_three_years_separately(site_name, season)
+    if not out:
+        return {}
+    save_phenocam_gcc_json(gcc_3y_path, out)
+    print(
+        f"[PhenoCam phenology] Fetched and wrote {gcc_3y_path} "
+        f"({len(out)} values for {season - 1}–{season + 1})"
+    )
+    return out
+
+
+def resolve_phenocam_gcc_for_timesat(
+    site_name: str, season: int, gcc_path: Path
+) -> dict[str, float]:
+    """
+    Load three-year series from ``phenocam_gcc_3y.json`` (or fetch once and
+    save there), merge with one-year ``gcc_path`` if present; three-year values
+    win on duplicate dates.
+    """
+    gcc_3y = gcc_path.parent / "phenocam_gcc_3y.json"
+    by_3y = load_or_fetch_phenocam_gcc_3y(site_name, season, gcc_3y)
+    by_1y: dict[str, float] = {}
+    if gcc_path.is_file():
+        try:
+            by_1y = load_phenocam_gcc(gcc_path)
+        except (OSError, json.JSONDecodeError):
+            pass
+    if by_3y:
+        return {**by_1y, **by_3y}
+    return by_1y
+
+
+def _day_count(calendar_year: int) -> int:
+    a = datetime(calendar_year, 1, 1)
+    b = datetime(calendar_year + 1, 1, 1)
+    return (b - a).days
+
+
+def daily_profile_for_year(by_date: dict[str, float], calendar_year: int) -> np.ndarray:
+    """
+    One value per day (length 365 or 366 for leap years). Gaps are filled by
+    linear interpolation in time along the year; if only one valid point exists,
+    that value is used for the whole year.
+    """
+    n = _day_count(calendar_year)
+    raw = np.full(n, np.nan, dtype=np.float64)
+    for d in range(1, n + 1):
+        dt = datetime(calendar_year, 1, 1) + timedelta(days=d - 1)
+        key = dt.strftime("%Y-%m-%d")
+        if key in by_date:
+            raw[d - 1] = by_date[key]
+    valid = np.isfinite(raw) & (raw > 0.0)
+    if not np.any(valid):
+        raise ValueError(f"No valid GCC in JSON for calendar year {calendar_year}")
+    if np.sum(valid) == 1:
+        v = float(raw[valid][0])
+        return np.full(n, v, dtype=np.float32)
+    idx = np.arange(n, dtype=np.float64)
+    raw = np.interp(idx, idx[valid], raw[valid])
+    return raw.astype(np.float32)
+
+
+def _gcc_profile_365_for_timesat(profile: np.ndarray) -> np.ndarray:
+    """TIMESAT uses 365 days per season; drop Dec 31 on leap years."""
+    p = np.asarray(profile, dtype=np.float32).ravel()
+    if p.size == 366:
+        return p[:365]
+    if p.size == 365:
+        return p
+    raise ValueError(f"expected 365 or 366 daily values, got {p.size}")
+
+
+def yyyydoy_to_iso(v: float) -> str:
+    x = int(round(float(v)))
+    y = x // 1000
+    doy = x - y * 1000
+    d = datetime(y, 1, 1) + timedelta(days=doy - 1)
+    return d.date().isoformat()
+
+
+def build_yraw_three_years(
+    by_date: dict[str, float], y1: int, y2: int, y3: int
+) -> tuple[np.ndarray, str]:
+    """
+    Stack three calendar years of daily GCC (365 pts/year) for TIMESAT.
+
+    If each of *y1*, *y2*, *y3* has at least one valid GCC in *by_date* (after
+    per-year gap filling), returns their concatenation — **three real years**.
+
+    If any of those years cannot be built (e.g. single-year download only),
+    falls back to **replicating** the profile for *y2* three times (legacy
+    TIMESAT workaround).
+    """
+    try:
+        p1 = _gcc_profile_365_for_timesat(daily_profile_for_year(by_date, y1))
+        p2 = _gcc_profile_365_for_timesat(daily_profile_for_year(by_date, y2))
+        p3 = _gcc_profile_365_for_timesat(daily_profile_for_year(by_date, y3))
+        yraw = np.concatenate([p1, p2, p3]).astype(np.float32, copy=False)
+        return yraw, "three_independent_years"
+    except ValueError:
+        p2 = _gcc_profile_365_for_timesat(daily_profile_for_year(by_date, y2))
+        yraw = np.tile(p2, 3)
+        return yraw, "single_year_replicated"
+
+
+def run_timesat_phenology_from_yraw(
+    yraw: np.ndarray,
+    years_triplet: tuple[int, int, int],
+    *,
+    start_cutoff: tuple[float, float] = (0.5, 0.5),
+    smooth_window: float = 2.0,
+    p_ignoreday: int = 366,
+) -> dict[str, str | float | None]:
+    """
+    Run TIMESAT on a length ``365 * 3`` daily VI stack and calendar *years_triplet*
+    (YYYY, YYYY, YYYY) for the time vector. Middle year in the triplet is the
+    season whose SOS/EOS we report.
+    """
+    yraw = np.asarray(yraw, dtype=np.float32).ravel()
+    y1, y2, y3 = years_triplet
+    nyear = 3
+    npt = 365 * nyear
+    if yraw.size != npt:
+        raise ValueError(f"yraw must have length {npt}, got {yraw.size}")
+    tlist: list[int] = []
+    for y in (y1, y2, y3):
+        t0 = datetime(y, 1, 1)
+        for d in range(365):
+            tlist.append(int((t0 + timedelta(days=d)).strftime("%Y%j")))
+    tv = np.array(tlist, dtype=np.int32)
+    if len(tv) != npt:
+        raise RuntimeError("internal: length mismatch")
+
+    vi = np.asfortranarray(yraw.reshape(1, 1, -1))
+    qa = np.asfortranarray(np.ones((1, 1, npt), dtype=np.float32))
+    lc = np.ones((1, 1), dtype=np.uint8)
+    landuse = np.ones(255, dtype=np.uint8)
+    p_out = np.arange(1, npt + 1, dtype=np.int32)
+    p_ylu = np.asfortranarray(np.array([0.0, 1.0], dtype=np.float64))
+    ci = 0
+    p_fitmethod = np.zeros(255, dtype=np.int32)
+    p_fitmethod[ci] = 1
+    p_smooth = np.zeros(255, dtype=np.float64)
+    p_smooth[ci] = float(smooth_window)
+    p_nenvi = np.zeros(255, dtype=np.int32)
+    p_nenvi[ci] = 1
+    p_wfact = np.zeros(255, dtype=np.float64)
+    p_wfact[ci] = 1.0
+    p_startmethod = np.zeros(255, dtype=np.int32)
+    p_startmethod[ci] = 1
+    p_startcutoff = np.zeros((255, 2), dtype=np.float64, order="F")
+    p_startcutoff[ci, :] = np.array(
+        [start_cutoff[0], start_cutoff[1]], dtype=np.float64
+    )
+    p_low = np.zeros(255, dtype=np.float64)
+    p_fillbase = np.zeros(255, dtype=np.int32)
+    p_seasonmethod = np.zeros(255, dtype=np.int32)
+    p_seasonmethod[ci] = 1
+    p_seapar = np.zeros(255, dtype=np.float64)
+    p_seapar[ci] = 1.0
+
+    if _timesat is None:
+        raise ImportError("Install the 'timesat' package: pip install timesat")
+    vpp, _vppqa, nseason, yfit, _yfitqa, _seasonfit, _tseq = _timesat.tsfprocess(
+        nyear,
+        vi,
+        qa,
+        tv,
+        lc,
+        1,
+        landuse,
+        p_out,
+        p_ignoreday,
+        p_ylu,
+        0,
+        p_fitmethod,
+        p_smooth,
+        NODATA,
+        45,
+        0,
+        p_nenvi,
+        p_wfact,
+        p_startmethod,
+        p_startcutoff,
+        p_low,
+        p_fillbase,
+        1,
+        p_seasonmethod,
+        p_seapar,
+        1,
+        1,
+        1,
+        npt,
+        len(p_out),
+    )
+    a = vpp[0, 0, :]
+    # three growing-season rows at indices 0, 13*2, 13*4 in the raw vector
+    middle_block = 2
+    off = 13 * middle_block
+    sosd = a[off + 0] if a.size > off + 0 else np.nan
+    sosv = a[off + 1] if a.size > off + 1 else np.nan
+    eosd = a[off + 3] if a.size > off + 3 else np.nan
+    eosv = a[off + 4] if a.size > off + 4 else np.nan
+    yfit_max = float(np.max(yfit)) if yfit.size else float("nan")
+
+    def pick(x: float) -> str | None:
+        if not np.isfinite(x) or x < 1.0e5 or x < 0:
+            return None
+        try:
+            return yyyydoy_to_iso(x)
+        except (OverflowError, ValueError):
+            return None
+
+    return {
+        "reference_calendar_year": y2,
+        "green_up_50pct_date": pick(sosd),
+        "green_up_50pct_fitted_gcc": float(sosv) if np.isfinite(sosv) else None,
+        "green_down_50pct_date": pick(eosd),
+        "green_down_50pct_fitted_gcc": float(eosv) if np.isfinite(eosv) else None,
+        "nseason": nseason[0, 0].tolist() if nseason.ndim >= 2 else [],
+        "yfit_max": yfit_max,
+    }
+
+
+def run_timesat_phenology(
+    daily_profile: np.ndarray,
+    years_triplet: tuple[int, int, int],
+    *,
+    start_cutoff: tuple[float, float] = (0.5, 0.5),
+    smooth_window: float = 2.0,
+    p_ignoreday: int = 366,
+) -> dict[str, str | float | None]:
+    """
+    Back-compat: run TIMESAT on one year’s 365(–366) profile **replicated** three times.
+    Prefer :func:`build_yraw_three_years` + :func:`run_timesat_phenology_from_yraw`.
+    """
+    prof = np.asarray(daily_profile, dtype=np.float32).ravel()
+    if len(prof) not in (365, 366):
+        raise ValueError("daily_profile must have length 365 or 366")
+    if len(prof) == 366:
+        prof = prof[:365]
+    yraw = np.tile(prof, 3)
+    return run_timesat_phenology_from_yraw(
+        yraw,
+        years_triplet,
+        start_cutoff=start_cutoff,
+        smooth_window=smooth_window,
+        p_ignoreday=p_ignoreday,
+    )
+
+
+def phenocam_gcc_path(site_name: str, season: int) -> Path:
+    return Path(f"data/{site_name}/{season}/raw/phenocam/phenocam_gcc.json")
+
+
+def phenocam_gcc_3y_path(site_name: str, season: int) -> Path:
+    return Path(f"data/{site_name}/{season}/raw/phenocam/phenocam_gcc_3y.json")
+
+
+def iter_sites_seasons_with_phenocam(
+    data_root: str | Path = "data",
+) -> list[tuple[str, int]]:
+    """``(site_name, season)`` for every ``phenocam_gcc.json`` under *data_root* (legacy)."""
+    root = Path(data_root)
+    if not root.is_dir():
+        return []
+    out: list[tuple[str, int]] = []
+    seen: set[tuple[str, int]] = set()
+    for p in sorted(root.glob("*/*/raw/phenocam/phenocam_gcc.json")):
+        rel = p.relative_to(root)
+        site, season_s = rel.parts[0], rel.parts[1]
+        if not season_s.isdigit():
+            continue
+        season = int(season_s)
+        key = (site, season)
+        if key not in seen:
+            seen.add(key)
+            out.append(key)
+    return out
+
+
+def iter_sites_seasons_from_sites_geojson(
+    path: str | Path = "data/sites.geojson",
+) -> list[tuple[str, int]]:
+    """
+    ``(sitename, season)`` from a GeoJSON FeatureCollection: each feature’s
+    ``properties.sitename`` and each key in ``properties.seasons`` (4-digit year).
+    """
+    path = Path(path)
+    if not path.is_file():
+        return []
+    with open(path, encoding="utf-8") as f:
+        fc = json.load(f)
+    out: list[tuple[str, int]] = []
+    for feat in fc.get("features", []):
+        props = feat.get("properties") or {}
+        name = props.get("sitename")
+        seasons = props.get("seasons")
+        if not name or not isinstance(seasons, dict):
+            continue
+        for skey in sorted(seasons.keys()):
+            if skey.isdigit() and len(skey) == 4:
+                out.append((str(name), int(skey)))
+    return out
+
+
+def write_phenocam_phenology_all(
+    *,
+    sites_geojson: str | Path | None = None,
+    data_root: str | Path = "data",
+    smooth_window: float = 2.0,
+    p_ignoreday: int = 366,
+) -> int:
+    """
+    Run :func:`write_phenocam_phenology_for_site` for every ``(site, season)`` in
+    *sites_geojson* (default: :file:`<data_root>/sites.geojson`), not a glob over
+    ``data/``.
+    """
+    geo = Path(
+        sites_geojson
+        if sites_geojson is not None
+        else Path(data_root) / "sites.geojson"
+    )
+    pairs = iter_sites_seasons_from_sites_geojson(geo)
+    if not pairs and geo.is_file():
+        print(
+            f"[PhenoCam phenology] No (sitename, season) entries in {geo} "
+            "(check properties.sitename and properties.seasons)."
+        )
+    elif not pairs:
+        print(f"[PhenoCam phenology] Missing or empty sites file: {geo}")
+    n = 0
+    for site, season in pairs:
+        print(f"=== {site} {season} ===")
+        write_phenocam_phenology_for_site(
+            site, season, smooth_window=smooth_window, p_ignoreday=p_ignoreday
+        )
+        n += 1
+    print(f"[PhenoCam phenology] Processed {n} site/season pair(s) from {geo}.")
+    return n
+
+
+def phenocam_phenology_path(site_name: str, season: int) -> Path:
+    return Path(f"data/{site_name}/{season}/raw/phenocam/phenocam_phenology.json")
+
+
+def write_phenocam_phenology_for_site(
+    site_name: str,
+    season: int,
+    *,
+    smooth_window: float = 2.0,
+    p_ignoreday: int = 366,
+) -> None:
+    """
+    If ``timesat`` is installed, build GCC from ``phenocam_gcc_3y.json`` (or fetch
+    three years once and save there), with optional one-year ``phenocam_gcc.json``,
+    then write
+    ``phenocam_phenology.json`` in the same directory with
+    ``green_up_50pct_date`` and ``green_down_50pct_date`` (ISO dates or null).
+    """
+    if _timesat is None:
+        out = phenocam_phenology_path(site_name, season)
+        print(
+            f"[PhenoCam phenology] Skipped (no timesat); would write {out}. "
+            "pip install timesat"
+        )
+        return
+    gcc = phenocam_gcc_path(site_name, season)
+    try:
+        by_date = resolve_phenocam_gcc_for_timesat(site_name, season, gcc)
+    except OSError as e:
+        print(f"[PhenoCam phenology] Skipped: {e}")
+        return
+    if not by_date:
+        g3 = gcc.parent / "phenocam_gcc_3y.json"
+        print(
+            f"[PhenoCam phenology] No GCC ({gcc} and no data in {g3} after API); "
+            f"skipping {phenocam_phenology_path(site_name, season).name}."
+        )
+        return
+    try:
+        yraw, stack_mode = build_yraw_three_years(
+            by_date, season - 1, season, season + 1
+        )
+    except (OSError, ValueError) as e:
+        print(f"[PhenoCam phenology] Skipped: {e}")
+        return
+    out = run_timesat_phenology_from_yraw(
+        yraw,
+        (season - 1, season, season + 1),
+        smooth_window=smooth_window,
+        p_ignoreday=p_ignoreday,
+    )
+    record = {
+        "green_up_50pct_date": out.get("green_up_50pct_date"),
+        "green_down_50pct_date": out.get("green_down_50pct_date"),
+    }
+    out_path = phenocam_phenology_path(site_name, season)
+    out_path.parent.mkdir(parents=True, exist_ok=True)
+    with open(out_path, "w", encoding="utf-8") as f:
+        json.dump(record, f, indent=2)
+        f.write("\n")
+    gup, gdn = record["green_up_50pct_date"], record["green_down_50pct_date"]
+    print(
+        f"[PhenoCam phenology] Wrote {out_path} (green-up {gup!r}, green-down {gdn!r}; "
+        f"TIMESAT input={stack_mode})"
+    )
+
+
+def main() -> None:
+    ap = argparse.ArgumentParser(
+        description="TIMESAT 50 % seasonal-amplitude green-up / green-down for PhenoCam GCC JSON."
+    )
+    ap.add_argument(
+        "--all",
+        action="store_true",
+        help="Write phenocam for every (sitename, season) in the sites GeoJSON (see --sites-geojson).",
+    )
+    ap.add_argument(
+        "--data-root",
+        type=Path,
+        default=Path("data"),
+        help="Resolves default --sites-geojson to <data-root>/sites.geojson.",
+    )
+    ap.add_argument(
+        "--sites-geojson",
+        type=Path,
+        default=None,
+        help="For --all: path to data/sites.geojson (default: <data-root>/sites.geojson).",
+    )
+    ap.add_argument(
+        "gcc_json",
+        type=Path,
+        nargs="?",
+        default=Path("data/innsbruck/2024/raw/phenocam/phenocam_gcc.json"),
+        help="Path to phenocam_gcc.json (default: Innsbruck 2024 if present).",
+    )
+    ap.add_argument(
+        "--season",
+        type=int,
+        default=None,
+        help="Calendar year to build the daily GCC profile (default: infer from file path .../<year>/...).",
+    )
+    ap.add_argument(
+        "--savitzky-hw",
+        type=float,
+        default=2.0,
+        help="Half-width for fitmethod 1 (Savitzky–Golay); default 2.",
+    )
+    ap.add_argument(
+        "--p-ignoreday",
+        type=int,
+        default=366,
+        help="TIMESAT p_ignoreday (default 366).",
+    )
+    ap.add_argument(
+        "-o",
+        "--output",
+        type=Path,
+        default=None,
+        help="Write results to this JSON file (same schema as stdout, plus metadata).",
+    )
+    ap.add_argument(
+        "--sidecar",
+        action="store_true",
+        help="Save two-date JSON next to input as phenocam_phenology.json (implies -o).",
+    )
+    args = ap.parse_args()
+    if _timesat is None:
+        raise SystemExit(
+            "The 'timesat' package is required. Install with: pip install timesat"
+        )
+    if args.all:
+        write_phenocam_phenology_all(
+            sites_geojson=args.sites_geojson,
+            data_root=args.data_root,
+            smooth_window=args.savitzky_hw,
+            p_ignoreday=args.p_ignoreday,
+        )
+        return
+    path: Path = args.gcc_json
+    if not path.is_file():
+        raise SystemExit(f"Not a file: {path}")
+
+    season = args.season
+    if season is None:
+        for part in path.parts:
+            if part.isdigit() and len(part) == 4:
+                season = int(part)
+                break
+        if season is None:
+            season = datetime.now().year
+
+    by_date = load_phenocam_gcc(path)
+    yraw, stack_mode = build_yraw_three_years(by_date, season - 1, season, season + 1)
+    out = run_timesat_phenology_from_yraw(
+        yraw,
+        (season - 1, season, season + 1),
+        smooth_window=args.savitzky_hw,
+        p_ignoreday=args.p_ignoreday,
+    )
+    payload = {
+        **out,
+        "source_gcc_json": str(path.resolve()),
+        "profile_year": season,
+        "timesat_input": stack_mode,
+        "method": "TIMESAT tsfprocess; startmethod=1; p_startcutoff=[0.5,0.5] (50% seasonal amplitude)",
+    }
+    out_path = args.output
+    if args.sidecar:
+        out_path = path.parent / "phenocam_phenology.json"
+    if out_path is not None:
+        out_path.parent.mkdir(parents=True, exist_ok=True)
+        to_write = (
+            {
+                "green_up_50pct_date": out.get("green_up_50pct_date"),
+                "green_down_50pct_date": out.get("green_down_50pct_date"),
+            }
+            if args.sidecar
+            else payload
+        )
+        with open(out_path, "w", encoding="utf-8") as f:
+            json.dump(to_write, f, indent=2)
+            f.write("\n")
+        print(f"Wrote {out_path}", file=sys.stderr)
+    print(json.dumps(payload, indent=2))
+    gup = out.get("green_up_50pct_date")
+    gdn = out.get("green_down_50pct_date")
+    if gup and gdn:
+        print(
+            f"Green-up (50 %): {gup}  |  Green-down (50 %): {gdn}  "
+            f"(profile year {season}, TIMESAT reference year {out['reference_calendar_year']})"
+        )
+
+
+if __name__ == "__main__":
+    main()
diff --git a/webapp/phenology.html b/webapp/phenology.html
new file mode 100644
index 0000000..2b63c43
--- /dev/null
+++ b/webapp/phenology.html
@@ -0,0 +1,145 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <meta charset="utf-8">
+    <title>Phenology</title>
+    <style>
+        body { margin: 0; font-family: sans-serif; }
+        .nav { margin-bottom: 15px; font-size: 14px; }
+        .nav a { margin-right: 12px; color: #0066cc; text-decoration: none; }
+        .nav a:hover { text-decoration: underline; }
+        .nav a.active { font-weight: bold; }
+        .container { max-width: 900px; margin: 0 auto; padding: 20px; }
+        h1 { font-size: 22px; margin-top: 0; }
+        .intro { font-size: 13px; color: #333; background: #fafafa; border: 1px solid #e5e5e5;
+                 padding: 10px 12px; border-radius: 4px; margin-bottom: 16px; line-height: 1.5; }
+        table { border-collapse: collapse; width: 100%; font-size: 13px; }
+        th, td { border: 1px solid #ccc; padding: 8px 10px; text-align: left; }
+        th { background: #f5f5f5; }
+        td.num { text-align: center; font-variant-numeric: tabular-nums; }
+        td.site { font-weight: 500; }
+        a.rowlink { color: #0066cc; text-decoration: none; }
+        a.rowlink:hover { text-decoration: underline; }
+        .empty { color: #666; }
+        .err { color: #a00; }
+        .loading { color: #666; }
+    </style>
+</head>
+<body>
+    <div class="container">
+        <div class="nav">
+            <a href="index.html">Full</a>
+            <a href="preselection.html">Pre-selection</a>
+            <a href="prepared.html">Prepared</a>
+            <a href="fusion.html">Fusion</a>
+            <a href="postprocessed.html">Postprocessed</a>
+            <a href="metrics.html">Metrics</a>
+            <a href="phenology.html" class="active">Phenology</a>
+        </div>
+        <h1>PhenoCam phenology (50% amplitude)</h1>
+        <p class="intro">
+            Green-up and green-down dates from <code>data/&lt;site&gt;/&lt;season&gt;/raw/phenocam/phenocam_phenology.json</code>
+            (TIMESAT on PhenoCam GCC). Site/season rows match <code>data/sites.geojson</code>.
+            Run <code>python phenology_timesat.py --all</code> or the pipeline to generate missing JSON files.
+        </p>
+        <p id="status" class="loading">Loading…</p>
+        <div id="tableWrap"></div>
+    </div>
+    <script>
+        function escapeHtml(s) {
+            return String(s)
+                .replace(/&/g, "&amp;")
+                .replace(/</g, "&lt;")
+                .replace(/>/g, "&gt;")
+                .replace(/"/g, "&quot;");
+        }
+
+        function cellDate(v) {
+            if (v == null || v === "") return "<span class='empty'>—</span>";
+            return escapeHtml(v);
+        }
+
+        async function loadPhenologyRow(site, season) {
+            const path = `data/${site}/${season}/raw/phenocam/phenocam_phenology.json`;
+            try {
+                const res = await fetch(path);
+                if (!res.ok) return { ok: false, up: null, down: null };
+                const j = await res.json();
+                return {
+                    ok: true,
+                    up: j.green_up_50pct_date ?? null,
+                    down: j.green_down_50pct_date ?? null
+                };
+            } catch {
+                return { ok: false, up: null, down: null };
+            }
+        }
+
+        async function main() {
+            const status = document.getElementById("status");
+            const wrap = document.getElementById("tableWrap");
+            let features = [];
+            try {
+                const res = await fetch("data/sites.geojson");
+                if (!res.ok) throw new Error("Could not load sites.geojson");
+                const g = await res.json();
+                features = g.features || [];
+            } catch (e) {
+                status.textContent = "";
+                status.className = "err";
+                status.textContent = "Failed to load data/sites.geojson.";
+                return;
+            }
+
+            const rows = [];
+            for (const f of features) {
+                const site = f.properties && f.properties.sitename;
+                if (!site) continue;
+                const desc = (f.properties && f.properties.description) || site;
+                const seasons = f.properties && f.properties.seasons
+                    ? Object.keys(f.properties.seasons).sort()
+                    : [];
+                for (const season of seasons) {
+                    rows.push({ site, season, desc });
+                }
+            }
+            rows.sort((a, b) => a.site.localeCompare(b.site) || a.season.localeCompare(b.season));
+
+            const results = await Promise.all(
+                rows.map((r) =>
+                    loadPhenologyRow(r.site, r.season).then((phen) => ({ ...r, ...phen }))
+                )
+            );
+
+            const head =
+                "<thead><tr>" +
+                "<th>Site</th><th>Season</th><th>Description</th>" +
+                "<th>Green-up</th><th>Green-down</th>" +
+                "</tr></thead>";
+            const body = results
+                .map((r) => {
+                    const q = new URLSearchParams();
+                    q.set("site", r.site);
+                    q.set("season", r.season);
+                    const viewer = `index.html?${q.toString()}`;
+                    return (
+                        "<tr>" +
+                        `<td class="site"><a class="rowlink" href="${viewer}">${escapeHtml(r.site)}</a></td>` +
+                        `<td class="num">${r.season}</td>` +
+                        `<td>${escapeHtml(r.desc)}</td>` +
+                        `<td class="num">${cellDate(r.up)}</td>` +
+                        `<td class="num">${cellDate(r.down)}</td>` +
+                        "</tr>"
+                    );
+                })
+                .join("");
+
+            status.textContent = "";
+            status.className = "";
+            wrap.innerHTML = "<table>" + head + "<tbody>" + body + "</tbody></table>";
+        }
+
+        main();
+    </script>
+</body>
+</html>