QGIS plugin

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QGIS plugin

The MonitorEO plugin computes time series, maps, trends and comparisons of the MonitorEO variables from a QGIS panel, over protected areas, ecoregions, the map view or your own layers. The maps arrive as GeoTIFF layers with values that you can query with Identify Features.

The options (variables, regions, metrics, filters, trends) are explained in Concepts.

Installation

1. Download monitoreo_qgis-<version>.zip from the latest release (under Assets).
2. In QGIS: Plugins > Manage and Install Plugins > Install from ZIP, choose the zip and click Install Plugin.
3. The MonitorEO button appears in the toolbar (and in the Web menu). Open the panel.
4. You can now compute: with the Project field empty, MonitorEO uses its shared account, without signing in. To compute with your Earth Engine account (and export to Google Drive), click Authenticate…, sign in with your Google account on the page that opens (once per computer; no terminal or earthengine authenticate needed) and type your project in Project.

The zip contains the monitoreo package and the Earth Engine library: there is nothing else to install. It works in QGIS 4.0.3 or later, on Windows, macOS and Linux (in QGIS 3, the plugin versions up to 0.3.3). To update, install the zip of the new version over the old one.

The panel

From top to bottom:

• Google Earth Engine: the Google Cloud project (empty: the shared account of MonitorEO), Connect and Authenticate…, and the bar of your EECUs spent this month (with the shared account, your research EECUs), with the level of your project and Check (see Concepts).
• Region: what to compute on.
• Variable: variable and sensor, period, another period to compare, season and per-pixel filters.
• Time series: step, metrics and the list of computed Series.
• Trends (Mann-Kendall and Sen): table of the region or map per pixel.
• Map: the variable summarized over time as a layer.
• Export to Google Drive: large maps and series.
• About MonitorEO: description, acknowledgements and links.

Each option has a ⓘ button to its right: when clicked, it explains the option in a few lines, with a link to its section of this manual. The one of Variable also describes the chosen variable: unit, pixel, dates and which filters can be applied to it.

The computations run as QGIS tasks (status bar, at the bottom): QGIS does not freeze meanwhile and several can be started at once. The warnings appear in the message bar, above the map, and stay in the Log Messages panel.

Tutorial: the NDVI of Sierra Nevada National Park

1. Connect

With the Project field empty, MonitorEO computes with its shared account: there is nothing else to do (Connect checks it). To use your account, type the identifier of your Earth Engine project in Project and click Connect; the first time on the computer, click Authenticate… first and sign in with your Google account in the browser (see Getting started). The project is remembered for next time.

The bar below tells you which part of your EECUs of this month you have spent; it is updated after each computation. With the shared account they are your research EECUs (25 EECU-h a month, for research only): if you have less than 10 % left, the message bar asks you to switch to your account, and when you have spent them the shared account does not compute for you until next month. With your own project, choose its level in the list (Community if you do not know).

2. Choose the region

In Region there are four options:

Option	What it uses
Layer (selected features or all)	A polygon layer of the project: the selected features or, if there are none, all of them. Name is the field with the name of each polygon; each one gives its own series.
Map extent	The rectangle you see on the map
Protected area (WDPA)	Type part of the name, click Search and choose the area in Area
Ecoregion at the center of the map	The RESOLVE 2017 ecoregion of the center of the view

For the tutorial: Protected area (WDPA), type Sierra Nevada, Search, and in Area choose Sierra Nevada · National Park · ESP · 859 km² (WDPA 389011). Look at the designation: the same name also has a natural park, a SAC and a SPA, with different boundaries.

3. Choose the variable and the period

• Variable: NDVI · Sentinel-2 · 10 m · S2_SR_HARMONIZED. Each entry gives the sensor, the pixel and the collection.
• Period: from 2023-06-01 to 2023-08-31 (summer 2023).
• Season: with the only box and two MM-DD dates, only those days of each year (useful in periods of several years).
• Remove pixels with: clouds, water, snow and aerosols, checked by default. With the NDSI uncheck snow and with the NDWI, water: they are what they measure. The last box removes the Sentinel-2 clouds with Cloud Score+; unchecked, with the Sentinel-2 scene classification (SCL).

4. Add the map

In the Map group: Metric Median, Temporal aggregation Whole period and Add the layer to the map.

When it finishes (about a minute) a layer appears with the median NDVI of each pixel, with the MonitorEO color ramp (stretched between the 5th and 95th percentiles), and the map is centered on the region. It is a temporary GeoTIFF with the values: activate Identify Features and click on the map to see the NDVI of a pixel (here, 0.65).

• The map is at the resolution of the data while the region has fewer than 4 million pixels; if not, with pixels 2, 3... times larger (the park, at 10 m, would have 24 million: it is downloaded at 30 m). For the full resolution, Export to Google Drive.
• Temporal aggregation: Whole period (the metric of all the images), Each year, then between years or Each month, then between years (the metric of each year or month and then the Metric between years). E.g. the median of the annual maxima: Metric Maximum, Each year, then between years, Metric between years Median.

5. Compute the time series

In Time series: Step Monthly, Metric of each step Mean (of the images of each month, in each pixel) and Statistic of the region Mean (of the pixels of the region). Change the period to 2022-01-01 – 2023-12-31 and click Compute the time series.

A window opens with the chart, the table (with the images and valid pixels of each value) and the buttons Save CSV… and Save chart…. Each computed series stays in the Series list: choose one and click Show to open its window again.

Steps: Monthly, Annual, 16 days or Daily (days with images). With a layer of several polygons, there is one line per polygon.

The map of each date: in the window of the series, Map of offers the map of the whole period and that of each date of the series: each month, year or 16-day block according to the Step (with the daily step, each month), with the Metric of each step. Choose one and click Add to the map. It arrives as a GeoTIFF with values, in a layer group with the name of the series, and all the maps of the series are painted with the colors of the first one so that they can be compared. Those of each date carry their days in the QGIS Temporal Controller: with several dates added, the controller shows them one after another, like an animation.

6. Trends

Has the vegetation of the park changed in the last 20 years, and in which months? For long series MODIS is advisable (since 2000): choose EVI · Modis · 250 m · MOD13Q1 or the NDVI, period 2005-01-01 – 2024-12-31.

In Trends (Mann-Kendall and Sen): Parts of the year Months, Metric of each year Mean and Trend table of the region. The window shows, for each month, its values of each year with the Sen line, and the table with the trend of each month: years with data, Kendall's τ, Z, p-value, whether it is significant (p < 0.05), Sen's slope per year and initial value.

In the example, the EVI rises in almost every month, but only significantly in August and September.

Trend map: choose the Part of the year of the map (a month, a 16-day block or the year), check if you want only pixels with a significant trend (p < 0.05) and click Trend map. A GeoTIFF is added with six bands per pixel: Sen's slope (the one that is painted, from red, decrease, to green, increase), τ, Z, p-value, initial value and number of years. Identify Features gives all six.

Also from the trends window: Map of offers the annual trend (that of the values of each year) and, with Parts of the year Months or 16 days, that of each month or block. Check Significant pixels only (p < 0.05) if you want and click Add to the map: the same six-band GeoTIFF is added, in a group with the name of the trends and with the colors of its first map, to compare the months with each other.

How they are computed and how to read them: Concepts.

7. Compare two periods

Check Compare with: other period and choose its dates. The Period above is the reference period. For example, reference 2005-01-01 – 2009-12-31 and the other period 2020-01-01 – 2024-12-31. With the box checked:

• Compute the time series compares the two periods: the mean of each month (or 16 days, or year, according to the Step) in each period, the reference in blue and the other in red, with the table of values and differences.
• Add the layer to the map adds the difference (other − reference) of the metric of the map, with the bands difference, reference and other.

8. Export to Google Drive

For large regions at full resolution or very long series: Resolution (empty, that of the data), Drive folder and Map (GeoTIFF) or Series (CSV). The panel follows the Earth Engine task and warns you when it finishes. If you have Google Drive for desktop, the GeoTIFF is loaded into the project as soon as it syncs. Exporting needs your account and your project: it is not possible with the shared account of MonitorEO, because the files go to the Drive of the account that computes.

Tips

• Start small: one year and a monthly step. Long periods with Sentinel-2 over large areas take minutes.
• Repeating is fast: Earth Engine caches what has already been computed.
• Several regions at once: select several polygons of a layer and choose their name field.
• Check Pixels and Images in the table: a month with few valid pixels (clouds, snow) is not very reliable.
• The maps are saved in a temporary folder of the system: to keep them, right-click the layer > Export > Save As….

If something fails: Troubleshooting.