Whether you’re a land steward on a dusty cattle ranch or navigating a cloud rainforest in the tropics, getting to know a landscape on the ground is an involved yet beloved process. Although nothing can replace a field visit, sometimes it can be tricky to get a broader perspective while down in the weeds.
And – there’s often that question in the back of your mind: what did this all look like in the past?
Aerial monitoring is one of the most efficient and effective ways to understand the history of a landscape. With countless data layers at your fingertips, Lens offers answers to your questions of what happened, where, and when?
This article will cover some of the Lens tools at your disposal and data layers you can add to your account to learn more about the history of landscapes.
Truecolor imagery displays ground conditions in a natural color palette, similar to what we observe in daily life. Lens offers several truecolor sources which vary in frequency, timing, and spatial resolution, giving you the ability to choose exactly what works best for your monitoring needs.
As soon as you upload an area of interest into Lens, public imagery sources will begin processing. In North America, USDA’s NAIP imagery offers free 1-meter resolution images dating back to about 2005. These images are useful for understanding the history of a property, and are perfect to use as Start Date images in Compare Mode, as seen below.
If your properties are in the tropics, Planet NICFI imagery will be automatically processed back through 2016.
For a more recent view of your property, explore the High-Frequency Sentinel-2 imagery from the European Space Agency. This free, global imagery is available back through late 2015. While having less spatial resolution than NAIP and commercial imagery sources, Sentinel-2 imagery comes into Lens every couple of days. You may find an image captured as recently as yesterday. This high refresh rate can help you narrow down when a particular change has happened, no matter whether it occurred last week or seven years ago. With a narrowed time window, you can order commercial imagery to take a closer look with higher resolution.
Landsat 8 (L8) from NASA and USGS provides 30-meter imagery extending back to 2013. Data is captured approximately every other week, making it an ideal source for tracking changes over time. This truecolor layer may be lower resolution compared to commercial sources, but can be useful for detecting landscape change or pinpointing the timing of a change.
In addition to public imagery sources, Lens allows you to easily order high-resolution, truecolor imagery for a variety of aerial vendors. These sources range from 0.3m resolution to 1.5m resolution, and provide the highest amount of detail for observing areas in Lens. With Compare Mode, you can compare an older NAIP or S2 image against a more recent commercial image. By default, these commercial images are displayed for the past two years. If you’d like for imagery to be processed further back, send us an email at lens@upstream.tech and we’ll help you out.
Changes in forest cover and vegetation can indicate a variety of events, such as drought, fire, disease, and logging. Many of these changes are best observed using Index layers and datasets, in addition to truecolor imagery.
To understand the history and extent of forest loss across a landscape, you can use the Global Forest Loss dataset. This annual dataset shows gross forest loss for each year between 2001 and 2022. In addition to viewing the layers individually or in Compare Mode, you can use Analyze Area to quantify the area of deforestation per year.
To take a closer look at a deforested area, you can view the S-2 Vegetation layer. The high frequency of Sentinel-2 helps narrow down the timing of when deforestation occurred. For concentrated events like logging or natural disaster, you can often narrow down a time frame to several days. When investigating broader trends like drought or disease, it may be helpful to view different years side-by-side to see longer-term changes.
Analyze Area can help you visualize trends in deforestation, drought, disease, and more. When you select an area, layer, and time frame, Analyze Area will compile the average value of each available Sentinel-2 sensing - giving you the broadest view into the history of changes in an area.
In the example below, I’ve used the Forest Loss dataset to visually identify an area of change. After selecting that area, I can see a predictable seasonal vegetation trend in the graph until June of 2021 - when this area was cleared. As shown by the post-disturbance trend line, this area has begun to recover in the years since as secondary succession vegetation takes hold. You may see a steeper recovery trend in restoration areas as new vegetation is planted.
You may be aware of past fire events on your properties, but unsure of exactly when and where they occurred. Or looking at truecolor imagery, it might be unclear whether a loss of vegetation was due to fire, logging, or other disturbance. Using the Burn Index (S2) layer, you can observe the extent, location, and timing of fire events. This layer can help distinguish a fire from other causes of disturbance, like drought, disease, or logging.
In addition to visually inspecting Burn Index layers, Analyze Area can shed light on the history of fire events within a particular area. In the example below, the graph indicates the timing of a fire that occurred in mid-2018.
Index layers can help you understand the history of flooding, seasonal precipitation trends, and other hydrologic events across your properties. While water can often be visible with regular truecolor S2 imagery, muddy floodwaters can be difficult to discern from the other Earth tones of a landscape. Even with 10-meter resolution, the S2 Surface Water layer easily distinguishes water from other land cover types.
Surface Water layers can be viewed in Compare Mode to quickly see past flood events.
By selecting the flooded extent of a river and analyzing Surface Moisture (S2), Analyze Area shows a history of seasonal hydrologic trends. In addition to these seasonal trends, I can see outlier points for flood events, which helps me understand the historic frequency of flooding on this property. To take a closer look at the associated index and truecolor imagery, I can click on the individual data points.
Sentinel-2 imagery is only captured when clouds are absent, so you might miss flood events that occurred under cloudy conditions - for instance flooding obscured by an overcast week following a hurricane. To understand the extent of flooding during these conditions, you can use the Sentinel-1 Surface Water dataset, which is derived from radar. This means that data is collected in any conditions, regardless of weather or time of day. Captured approximately every 12 days, Sentinel-1 data extends back until 2014.
For a view into the recent history of land cover changes, you can use Analyze Area with Impact Observatory’s Land Cover Land Use dataset. This dataset displays a global map of land use/land cover derived from ESA Sentinel-2 imagery at 10m resolution for 2017 - 2022. As shown below, hovering over each year in the Analyze Area graph will display an area breakdown of each type of land cover. This dataset is handy for quantifying changes in area of various land covers over time.
Lens also offers 30m National Land Cover Database data, which extends back to 2001 and can also be used with Analyze Area to understand historical changes in land cover.
Many of us are familiar with the difficulties of interpreting baseline reports that rely on non-georeferenced photos, or worse yet: no visuals at all. With the reporting capabilities of Lens, you can easily create baseline reports to document the prior conditions of a landscape with aerial imagery and photos from the field. Reports generated using Lens may be used internally, or distributed to entities such as the Land Trust Accreditation Commission, landowners, legal counsel, contractors, and government or non-profit collaborators.
Lens reports summarize the notes that you create in Lens. Each note includes the data layers being viewed when the note was created, in addition to any interpretation text. By using the polygon tool to create your note, you can easily estimate the acreage of an area (which can be tricky to do in the field). It’s particularly helpful to attach photos from the field to your notes in Lens, as these will be appended to generated reports. To learn more about creating notes in Lens, see our support article here.
Reports can be generated via the blue Report button at the top of the Notes pane. On the first page of a report, there is a freeform text box where you can include general information or paste form text from a monitoring report. Each note will appear as a page in the report, and these pages can be re-ordered or hidden from the report. To learn more about customizing reports, see our article here.
Hop into Lens and start monitoring! You can't break anything, so click around and start learning about the history of your landscapes .
As questions come up, our Knowledge Base has all of the answers you're looking for. You can click on your name in the top right corner and navigate to our support docs from there.
If you aren't finding the answers to your questions, don't hesitate to reach out to us at lens@upstream.tech. We're here to help. Happy monitoring!
