Monitor conservation easements

Last updated: May 17, 2023
May 17, 2023
Table of contents

Landscapes are constantly changing, especially when humans are involved. Even with field photos and reports from past years, it can be tricky to keep track of when various changes occur on a property. "Was that shed there two years ago?" "Was that driveway expanded or are my eyes playing tricks on me?" These are questions I often asked myself while monitoring conservation easements on the ground during my days as a steward.

When it comes to quickly identifying areas of change on conservation easements, there's no better tool than Lens. Whether you're spotting reserved right development, agricultural activity, or easement violations, Lens is a powerful tool for identifying changes and prioritizing your time in the field. This guide will cover some best practices for monitoring easements via Lens.

What follows is a series of steps I recommend for land trust stewards to use when monitoring conservation easements in Lens. I'll walk through the main tools in your toolbox and how to use them to answer stewardship questions and conduct remote monitoring.

1. Choose an Image

Credit: "Remote Property Monitoring at The Nature Conservancy in California", Fall 2020

Your first step is to get the imagery you need based on the timeframe of your monitoring. This could mean imagery from this calendar year if you’re conducting annual monitoring, or it could mean imagery from a few years back for setting a baseline. Lens allows you to easily order high-resolution, truecolor imagery from a variety of aerial vendors. When monitoring easements, it's typically best to use the highest-resolution imagery available to give you the best chance of spotting prohibited uses or activities.

From the Order pane, you can see a spatial resolution for each option in the list. Spatial resolution describes the size of the pixel. For example, 1-meter resolution imagery such as NAIP means each pixel covers a 1 by 1 meter square of the earth. Smaller pixels capture a clearer picture and can identify smaller features. The Nature Conservancy published their findings on spatial resolution needs for various monitoring criteria, which is helpful consideration for choosing the right image for easement monitoring.

Larger scale activities like forestry activity can be spotted with high-frequency Sentinel-2 data, which is freely available in Lens. But, for spotting new structures, ATV tracks, new fences, etc., sub-meter commercial imagery is best.

Image resolutions from various sources in Lens

2. Monitor in Compare Mode

Compare Mode in Lens showing 2020 USDA NAIP imagery and 2022 Airbus imagery on the right 

While looking at one image is helpful, seeing two side-by-side is even better. Compare mode makes it easy to observe changes over time. Enter Compare mode and select a Start Date image that corresponds to what you'd like to use as your baseline--maybe a time around the easement signing date, or when you'd last visited the property.

Select a recent high-resolution image to use as your End Date image. Typically you'll want this to be as recent as possible while meeting your spatial resolution needs. With these images, you can move the slider bar back and forth to easily spot changes. Alternatively, you can press the H and L keys to flicker the bar back and forth.

3. Use Public Imagery Sources

In addition to the high-resolution commercial imagery that is available for purchase through Lens, we automatically provide available public remote sensing data to all Lens users at no cost. This includes 1-meter resolution USDA NAIP aerial flyover data going back to approximately 2003, as well as 10-meter resolution Sentinel-2 imagery from the European Space Agency.

NAIP imagery is only captured every few years and is made publicly available with a slight delay, meaning it isn’t useful for the current monitoring year. However, it serves well as a baseline Start Date image in Compare mode. With 1-meter resolution, it's crisp enough for monitoring purposes.

Monitoring for vegetation changes using Sentinel-2 Vegetation Layers in Compare mode

Sentinel-2 (S2) imagery from the European Space agency is a high-frequency option in the Layer dropdown. At 10-meter resolution, it's less-than-ideal for most easement monitoring purposes. But, S2 imagery comes into Lens every five days or so, making it a fantastic tool for narrowing down the time window of when exactly a change has occurred. Then you can order high-resolution imagery for further investigation of what happened. The S2 vegetation layer is particularly handy for spotting larger-scale vegetation changes like forestry work or road clearings.

4. Monitor for Reserved Right Activity

New structures spotted in Compare mode. Left: NAIP 2018. Right: Airbus 2021

Some easements require more visits than others, and remote monitoring is the easiest way to frequently check properties at higher risk of development.

Once you have a recent, high-resolution image, you can start spotting changes. Monitoring for changes is best done in compare mode using a Start Date image from the last time you monitored the property.

New structures, roads, and disturbances will be visible as you move the slider bar back and forth. On the right, you can see several new buildings that were constructed between the image dates. Using high-frequency Sentinel-2 data, we can narrow down the time range of when this work occurred.

5. Make Notes and Generate Reports

Creating a new note polygon. Notice that the polygon's area is automatically calculated in acres, which is handy for estimating impacted area size. Imagery copyright Airbus 2022.

When there's an area you'd like to document, create a note from the left side panel. Notes allow you to document what you're observing about a property.  You can also upload photos to each note from site visits. Because each note is saved with the related data layers and the author is named, you and your team members can easily refer back to observations over time for efficient collaboration.

All of this information is then captured when you generate a report in Lens. From the Notes pane, simply click the “Create Report” button at the top. Once you've opened the report builder, there's a variety of ways you can modify your Lens reports to suit your needs. See this article for the details.

6. View Overlays and Building Envelopes

To help visualize where development should and shouldn't be occurring, you can add building envelopes and other features into Lens as overlays. These overlays can be toggled on and off to identify building envelopes, exclusion areas, and photo points at a glance. Overlays are customizable in color, fill, and default appearance.

A building envelope displayed overtop an easement as an Overlay. Imagery credit: Nearmap 2022

In addition to visualizing building envelopes, overlays can be a great way to delineate areas of disturbance to track recovery over time. Beyond the custom overlays that you can upload into Lens, we also offer overlays included with your subscription that can be viewed in the Lens Library such as USGS Flowlines, Microsoft Building Footprints, and Parcel Data.

7. Examine Agricultural Activity

Identifying agricultural management trends over time can be an important part of monitoring easements. Spotting new field development, erosion issues, water usage, and other monitoring criteria is simple with Lens. Let's take a look at some examples.

Below, Compare mode is being used to identify center-pivot irrigation. Having imagery from past years provides context for how often fields are put into production, cover crop presence, green-up, and more.

Observing a center pivot using truecolor imagery in compare mode. Imagery credit: USDA NAIP

In addition to high-resolution commercial and NAIP imagery, use the high-frequency Sentinel-2 (S2) imagery to narrow down the time interval of when planting and harvest has occurred.

While a drive-by visit of this pivot would identify that the field is in use, ground-level isn't always the best vantage point for seeing the big picture. It may be tricky to tell if the entire pivot area is being irrigated or if there's any areas where the crops may be struggling. That's where Lens comes in.

Below, the same pivot is being observed in the NAIP Vegetation Layer. In this view, we can see a patch of the field that has less vegetation vigor, possibly signaling a water issue, nutrient deficiency, pest, or other disturbance.

Observing a center pivot and a disturbed area using Vegetation Index imagery in compare mode. Imagery credit: USDA NAIP

8. Analyze Areas

Using Analyze Area to determine the timing of a timber harvest. Imagery credit: Airbus 2022

The Analyze Area tool allows you to easily visualize seasonal patterns and year-over-year changes in ecological conditions. Select a specific area of interest within a property and see how conditions have changed over the last several months or years. This feature can be used in a variety of applications, such as determining the timing of a timber harvest by reviewing seasonal cycles in vegetation vigor, or visualizing fluctuations in water and surface moisture presence in wetland areas.

Since the tool uses high-frequency data, it's a great way to answer the question of when a particular change happened. In the example on the right, I've selected an area of forest that was cleared sometime in the past couple years. By viewing the graph of vegetation trends, I can see when exactly the area was cleared. This insight can inform the time frame for ordering high-resolution imagery to take a closer look.

9. Subscribe to Vegetation Alerts

Vegetation Alerts on an enrolled property in Lens

Our automated alerts serve as a second set of eyes on your properties. Vegetation Alerts are designed to support Lens Plus and Enterprise customers monitoring large properties or portfolios, ensuring that they can quickly review and respond to changes. For enrolled properties, vegetation alerts identify areas where a significant decrease in vegetation vigor has occurred compared to the same period in prior years.

This tool helps spot changes that may occur after a monitoring visit. For instance, if a landowner removed an area of forest a week after a monitoring visit, that change may go undetected until the next year. With Vegetation Alerts, we'll keep an eye on your properties year-round.

10. Monitor for Ownership Changes

Parcel Data Overlay in Lens

Verifying ownership is an important part of easement monitoring, but it's typically time-intensive due to bouncing between various county assessor sites. There's two ways that Plus and Enterprise customers can easily monitor for ownership changes and subdivisions in Lens.

The parcel data overlay allows for parcel data to be streamed from Regrid, our data partner. The overlay can be turned on from the Overlays menu, and displays ownership data overtop of your properties in Lens so that you can verify ownership at a glance.

Click on the left side of the overlay button to customize appearance and fill preferences.

In addition to manually verifying ownership in Lens, you can enroll properties into Parcel Owner Alerts to automate the process. For enrolled properties, we’ll check for any changes at the start of each quarter, and create a new alert with details on the new owner for each tax parcel, as well as sale date if available. This is a great way to keep a second set of eyes on your properties for ownership changes, year-round.

Parcel Owner Alerts in Lens

11. Consider Remote Monitoring Standards

Before you dive into monitoring for the season, here's a couple of checklist items to consider.

  • The Land Trust Alliance requires in-person monitoring visits at least once out of every five years. Depending on your properties, you may want to visit in-person more frequently. Read more here.
  • Whether you're monitoring remotely or in person, make sure that the methods you choose align with any internal guidance from your organization. And, be sure that your monitoring methods can adequately answer the specific stewardship questions you have for a given property.
  • Monitoring doesn't always go to plan, and remote monitoring can help complement an in-person visit. For instance, if there's deed terms regarding haying at a certain time of year and you couldn't make it out on site then, use recent imagery to fill in any gaps from your field visit.

What Next?

Hop into Lens and start monitoring! You can't break anything, so click around and start checking out your easements.

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 We're here to help. Happy monitoring!