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The three types of optical remote sensing?
essential sensors
  • 📊 Multispectral — a few broad discrete bands
    • Examples: Landsat OLI, SPOT HRV, IKONOS, MODIS
    • Typical: 4–10 bands across visible + NIR + SWIR
  • 🔥 Thermal — one or more bands in 3–14 µm IR
    • Examples: Landsat TIRS, ASTER thermal
    • Detects emitted heat (works day and night)
  • 🌈 Hyperspectral — hundreds of narrow contiguous bands
    • Examples: Hyperion (220 bands), AVIRIS
    • Identifies specific minerals, plant species, pollutants
💡

Multi = few (tens), Hyper = many (hundreds), Thermal = heat only. 'Hyper' literally means MORE — that's the clue.

sensors/three-optical-types ✎ edit content

Across-track vs along-track scanners — examples?
essential sensors

Two scanning geometries used by multispectral sensors:

  • 🔄 Across-track (whiskbroom)
    • How: discrete detectors + scanning mirror sweeps perpendicular to flight
    • Examples: Landsat MSS, TM, ETM+
    • Drawback: moving mirror = mechanical wear
  • ➡️ Along-track (pushbroom)
    • How: linear array of detectors — no moving parts
    • Examples: SPOT HRV, IRS LISS, IKONOS, QuickBird, Landsat 8/9 OLI
    • Wins on: longer dwell time → better SNR, more reliable
💡

Whiskbroom WIGGLES a mirror (Landsat 1–7). Pushbroom PUSHES a linear array straight ahead (SPOT, IKONOS, Landsat 8/9 OLI). No wiggle, no breaking part.

sensors/scanner-geometries ✎ edit content

IKONOS — altitude, bands, radiometric resolution?
essential sensors
  • 🛰️ Orbit
    • Altitude: 681 km
    • Sun-synchronous, 10:30 AM equator crossing
  • 📷 Bands
    • 🩶 Panchromatic (0.45–0.90 µm) → 1 m detail
    • 🟦🟩🟥🟪 Multispectral 4 bands (Blue/Green/Red/NIR) → 4 m detail
    • Pan-sharpening fuses them → effective 1 m color
  • 🎚️ Radiometric: 11-bit → 2 048 grey levels
  • 🎯 Off-nadir pointing: up to ±45° (along + across track)
  • 🏆 Heritage: first U.S. commercial sub-meter satellite (1999–2015)
💡

IKONOS = 1 meter pan, 4 meter MS, 11-bit, at 681 km. Sub-meter commercial pioneer. Tilts ±45° (more than SPOT's ±27°).

sensors/ikonos-key-facts ✎ edit content

SPOT 1–3 — altitude, bands, orbit?
essential sensors
  • 🛰️ Orbit
    • Altitude: 832 km
    • Sun-synchronous, 10:30 AM equator crossing
  • ⏱️ Revisit
    • Nadir: 26 days
    • With off-nadir tilt (±27°): 1–4 days at mid-latitudes
  • 📷 Bands — no blue!
    • 🩶 Panchromatic (0.51–0.73 µm) — 10 m
    • 🟩 XS1 — Green (0.50–0.59 µm) — 20 m
    • 🟥 XS2 — Red (0.61–0.68 µm) — 20 m
    • 🟪 XS3 — NIR (0.79–0.89 µm) — 20 m

⚠️ No blue band on SPOT 1–3 → can’t make natural-color composites.

💡

SPOT 1-3: 832 km (higher than IKONOS 681), 10 m pan / 20 m MS, no blue (Green-Red-NIR only). Off-nadir ±27°. French (CNES).

sensors/spot-key-facts ✎ edit content

Hyperion (on EO-1) — specs?
likely sensors
  • 🛰️ Platform: EO-1 satellite
  • 🌈 Bands: 220 (hyperspectral), covering 0.4 – 2.5 µm
  • 🎯 Spatial resolution: 30 m
  • 📐 Orbit altitude: 705 km
  • 🔬 Use: mineral ID, species mapping, pollutant detection via spectral matching

⚠️ The hallmark of hyperspectral: hundreds of narrow contiguous bands (vs. multispectral’s handful of broad bands).

sensors/hyperion-specs ✎ edit content

Pushbroom over whiskbroom — four advantages + one disadvantage?
likely sensors

✅ Advantages - ⚙️ No moving mirror → more reliable, longer mission life - ⏱️ Longer dwell time per pixel → better signal-to-noise - 📦 CCDs are smaller, lighter, lower power than scanning optics - 🎯 More accurate radiometry per detector

❌ Disadvantage - 🎚️ Calibrating thousands of detectors uniformly is hard — each CCD has slightly different gain/offset

sensors/pushbroom-advantages ✎ edit content

What does a sun-synchronous orbit guarantee?
likely sensors

A near-polar orbit tuned so the orbital plane precesses at Earth’s orbital rate around the Sun.

  • 🛰️ Result: satellite crosses the equator at the same local solar time every day (typically 9:30 – 10:00 AM)
  • 🌅 Why it matters: consistent sun angle → comparable imagery across dates
  • 📷 Used by: Landsat, SPOT, IKONOS, Sentinel-2 — basically every Earth-observing land sensor
sensors/sun-sync ✎ edit content

SPOT HRV off-nadir capabilities?
likely sensors
  • 🪞 Steerable mirror tilts up to ±27° from vertical
  • 📐 Stereoscopic imagery — two views from different angles → parallax → 3D / DEMs
  • ⏱️ Revisit boost — 26-day nadir cycle → 1–5 days at mid-latitudes
  • 🌍 Swath access — can image ~900 km on either side of the ground track

IKONOS does the same but with a wider tilt range (±45°).

sensors/spot-offnadir ✎ edit content

SPOT 1–3 MS bands?
maybe sensors

All multispectral bands at 20 m:

  • 🟩 XS1 — Green, 0.50–0.59 µm
  • 🟥 XS2 — Red, 0.61–0.68 µm
  • 🟪 XS3 — NIR, 0.79–0.89 µm

Also: 🩶 Pan 0.51–0.73 µm at 10 m.

⚠️ No blue band on SPOT 1–3 → no natural-color composites.

sensors/spot1-3-bands ✎ edit content

WGS 84 — key facts?
maybe sensors
  • World Geodetic System 1984 — global coordinate/datum standard.
  • Reference surface: spheroidal ellipsoid.
  • Origin: Earth’s center of mass, accurate to ~2 cm.
  • Used by GPS/GNSS and nearly all modern RS products.
sensors/wgs84 ✎ edit content

WGS 84 — coordinate origin accuracy?
probably not sensors

Coordinate origin (Earth’s center of mass) is defined to within about 2 cm.

sensors/wgs84-accuracy ✎ edit content

IKONOS successors — the current sub-meter commercial satellites?
probably not sensors
  • WorldView-1/2/3/4 (Maxar)
  • GeoEye-1 (same operator)
  • Pleiades 1A/1B (Airbus)
  • SkySat (Planet) — 0.5 m, daily revisits

All inherit IKONOS’s tasked sub-meter commercial model.

sensors/ikonos-successors ✎ edit content