Area Monitoring

Satellite Area Monitoring

Draw any area on the map. The satellite keeps watching. Track how a place changes over time — automatically, with no GIS software and no code.

Quick answer — what Off-Nadir Delta is

Satellite area monitoring means repeatedly observing a fixed area with satellite imagery to detect change over time. You draw a polygon, choose a metric (NDVI, SAR backscatter, NDWI), and a time series is built automatically. Off-Nadir Delta does this in the browser — no GIS software, no code — and flags anomalies when readings depart from the area\u2019s own recent history.

Draw & Watch

Draw any polygon on Earth and the area is monitored continuously — no manual re-checking.

Automatic Time Series

Every satellite pass is analyzed and appended to a continuous time series of your chosen metric.

Anomaly Alerts

Readings that depart from the area\u2019s own recent history are flagged so change never slips past you.

Multi-Index

Track several indices over the same area to tell different change events apart with confidence.

All-Weather

Sentinel-1 SAR monitoring sees through clouds, day or night, so coverage continues during storms.

No GIS, No Code

Everything runs in the browser. No QGIS, no Earth Engine scripts, no downloads — just draw and go.

What Is Satellite Area Monitoring?

Satellite area monitoring is the practice of repeatedly observing the same geographic area with satellite imagery to detect and measure how it changes over time. Rather than interpreting a single snapshot, you build a time series of a chosen metric for a fixed polygon — so trends, seasonal cycles, and sudden events all become visible and quantifiable.

The metric you track depends on what you care about. NDVI and related indices follow vegetation health; SAR backscatter follows surface and structural change and works through clouds; NDWI follows water extent; and nighttime lights follow human activity. Tracking several at once — multi-index monitoring — lets you distinguish, for example, a harvest from a flood from deforestation.

Historically this required desktop GIS or code-based platforms. The shift that matters is no-code, browser-based monitoring: you draw an area, pick what to track, and the system handles imagery search, computation, time-series assembly, and anomaly detection for you. See the full step-by-step guide.

Two ways to keep watching a place

“Monitoring” covers two different jobs, and picking the wrong one is why a watch either says nothing or says too much. A monitored area measures a number over a polygon and tells you when that number becomes unusual. A standing ordersaves a question about an area and tells you when something happens there worth reading. Both are free to set up, and both charge only when work actually runs.

Monitored area vs standing order

Facts last reviewed 2026-08-23.

Aspect	Monitored area	Standing order
What it watches	A measurement over a fixed polygon	Events inside a bounding box
What you configure	The area and the index to track	A question, a scope, and what counts as significant
What makes it run	A new usable satellite pass over the area	A daily, weekly, or monthly check
What you get back	A time series, with unusual readings flagged	An AI analyst brief, and an email if you asked for one
Cost to create	Free	Free
When it meters	When new imagery is measured	When a check fires — quiet checks cost nothing
Available over API and MCP	Yes	Yes
Answers	“Has this surface changed?”	“Has anything happened here?”

Both are also available outside the browser: the REST API and the MCP server can create either kind of watch, list what is being watched alongside what your plan still allows, and read a monitored area’s full measurement history. How many you can run at once depends on your plan.

How It Works

Draw Your Area

Pan to any location on Earth and draw a polygon around the area you want to watch — a field, forest, coastline, construction site, or city block.

Choose What to Track

Pick one or more satellite indices — NDVI for vegetation, SAR backscatter for all-weather surface change, NDWI for water, nighttime lights, and more.

Let Satellites Watch

Each time a satellite passes over, the area is re-analyzed automatically and added to a continuous time series — no manual checking.

Get Alerted to Change

When a reading departs from the area’s own recent history, it is flagged so you can investigate what changed and when.

Frequently Asked Questions

What is satellite area monitoring?▼

Satellite area monitoring is the practice of repeatedly observing a fixed geographic area with satellite imagery over time to detect and measure change. Instead of viewing a single image, you build a time series of a chosen metric — such as NDVI (vegetation), SAR backscatter (surface/structure), or NDWI (water) — for the same polygon, so gradual or sudden changes become visible and measurable.

Can I monitor an area without GIS software?▼

Yes. Traditional area monitoring required desktop GIS (like QGIS or ArcGIS) or code-based platforms (like Google Earth Engine). Off-Nadir Delta runs entirely in your browser: you draw an area, choose what to track, and the time series is built automatically — no installation, no scripting, and no data downloads.

How does automated change detection work?▼

For each new satellite pass, the selected index is recomputed over your area and compared against its own recent history. A reading is flagged when its modified z-score exceeds 3.5 — that is, when it sits far from the MEDIAN of the last 30 measurements, expressed in units of median absolute deviation (MAD). Median and MAD are used rather than mean and standard deviation because one extreme reading inflates a standard deviation and so raises the very bar it is judged against; the robust statistic does not move. At least 5 measurements are required before anything is flagged.

Which satellites and indices can I monitor?▼

Common choices include Sentinel-2 optical indices (NDVI, EVI, SAVI, NDWI, NDBI, NBR), Sentinel-1 SAR backscatter (VV/VH, works through clouds day or night), and VIIRS nighttime lights. Combining multiple indices over the same area — multi-index monitoring — lets you tell different change events apart.

What can satellite area monitoring be used for?▼

Typical uses include tracking deforestation and forest health, monitoring crop growth and irrigation, detecting flooding, watching construction and urban expansion, observing coastline and water-body change, and verifying environmental compliance. Any area whose surface changes over time is a candidate.

How often is an area updated?▼

Update frequency depends on the satellite. The Sentinel-2 constellation revisits the same spot roughly every 5 days at the equator and more often at higher latitudes, and Sentinel-1 SAR every 6 days with the two-satellite constellation (12 days from a single satellite). A cloudy optical pass yields no usable reading, so the effective optical cadence is lower than the nominal revisit; SAR is especially valuable here because it is not blocked by clouds, so monitoring continues during storms and at night.

Is satellite area monitoring free?▼

You can start free. Off-Nadir Delta offers a free tier to set up and run area monitoring, with paid plans raising how many areas you can monitor at once and unlocking the rest of the platform. See the pricing page for current details.

What is the difference between a monitored area and a standing order?▼

They watch different things. A monitored area measures a quantity — an index such as NDVI or SAR backscatter — over a fixed polygon, re-measuring on each new usable satellite pass and flagging readings that depart from the area’s own history. A standing order watches an area for events: you save a question and a bounding box with a daily, weekly, or monthly cadence, and when new activity in that area meets your thresholds it runs an AI analyst brief and can email you. One answers "has this surface changed?"; the other answers "has anything happened here worth reading about?" Both are free to create, and both are metered only when work actually runs.

When does continuous monitoring cost tokens?▼

Creating a monitored area or a standing order costs nothing, and neither does listing what you have set up. Tokens are consumed only when work actually happens: a monitored area meters when new imagery is measured, and a standing order meters when a check fires and an analyst brief is produced. Checks that find nothing above your thresholds are recorded as quiet checks and cost nothing, so a watch over a quiet area is cheap to leave running.

Can I set up and read monitoring programmatically?▼

Yes. Both kinds of watch are available over the REST API and the MCP server, not just in the browser: you can create a monitored area or a standing order, list what is being watched together with what your plan still allows, and read the full measurement time series for one area. That makes it possible to drive continuous monitoring from your own pipeline, or to let an AI agent set up and read a watch on your behalf.