Undoubtedly the best case scenario while working with satellite imagery is to find the most suitable images for your use-case from, let’s say, Sentinel-2 or Landsat-8, which reliably covers your area of interest (AOI); therefore allowing you to quickly get accurate and valuable data as a result of processing.
Occasionally some sections of your AOI, most notably in large AOI’s that cover several scenes, as well as AOI’s which are located near or on the edges of scenes may remain beyond the boundaries of the current zone. These compilation image-stitching issues may lead to partial analysis and loss of valuable insight.
To resolve image-stitching issues, Mosaic was born.
Mosaic was designed from the ground up as an easy-to-use feature that allows сombining, merging, and visualizing grouped scenes from one sensor, in one image, for your specific AOI and required data time frame.
All of the scenes available for the required date are combined, and the AOI is 100% covered
The solution is so simple and effective that it’s incredibly surprising it hasn’t been done before.
Basic Mosaic Concepts Available in GIS tools
There are several approaches to creating your own Mosaic, you can quickly choose the most suitable for your needs.
- Global Mosaic coverage
- Mosaic is combined from all of the satellite passes per day
- Mosaic is being created strictly within the set area of interest (AOI)
How Mosaic works in LandViewer
LandViewer (LV) in turn, offers a combination of approaches, that is, the user draws the AOI. Subsequently, the system fits the AOI into a bbox - the specific geometry outlined around the AOI, according to which the images will be rendered. For instance, in the case that an AOI is circular , the mosaic will be rendered within the outlined square.
Depending on the way the AOI is set, the user will get one of the following results:
- If you drop a pin on the map, the software will generate a list of individual scenes, just as it did before
- If you draw a large AOI, or an AOI which is located on the border of two or more scenes, Mosaic will populate in the search results
The only condition for launching Mosaic is your AOI
Once you have drawn your AOI that covers the several scenes, have filtered out cloudiness, and set the desired angle of the sun, the system displays the search results of the Mosaic with a preview generated according to the set parameters automatically. The number of scenes in the Mosaic are specified on the preview cards.
Key Mosaic Capabilities
And, we have come down to the most important point, that is - what else can we do with Mosaic? So, once we’ve viewed the Mosaic on the map, we are able to proceed with the following options:
Processing in Browser:
- Apply indices and band combinations - both default and custom
- Set Brightness and Contrast stretching
Analytics in Browser (Coming Soon)
- Monitor and measure how the attributes of a particular area have changed between two or more time periods with the Change Detection function
- Perform effective zone management according to the index value ranges, using the Clusterization feature.
- Check the vegetation growth dynamics for your area of interest (AOI) over a long period of time with the Time Series options
- Сreate engaging GIF’s or video stories and share your data with other users online with the Time-lapse animation.
The Download Options Available in LandViewer
Three types of downloads can be applied to Mosaic, these are - Visual, Analytics, or Index, depending on the user's request.
NB: The user selects the "Mosaic" or "Fragments of bulk" download type. The difference between these two options lies in the final data, that will be presented to the user - the system downloads the merged scenes with the "Mosaic" download option; the system downloads fragments of scenes as a list if the "Fragments of bulk" parameter is selected.
Visual: In the event that you select the Visual type, the resulting data will be delivered in JPEG, KMZ, and GeoTIFF file formats containing the merged scenes (e.g. all of the scenes that fall into the AOI and don’t intersect).
Analytics: The download result with Analytics selected will be an archive of the merged bands, without metadata (for example [GeoTiff1: B02, GeoTiff2: B03, GeoTiff3: B04, GeoTiff4: B05.]).
With the Index type, the resulting data for the Mosaic will be presented as a TIFF file
Indexes Take note of the "Download by crop" option. The cropping of a mosaic is performed in accordance with the user’s parameters, i.e. bbox geometry specified by the user. In situations where the crop parameters are not set, all scenes are fully downloaded.
Mosaic in practice
Use -case 1 - Construction development monitoring, Dubai
Objective: To detect progress in construction development of a large area of interest (AOI)
Target audience: All Construction Industry Companies
Problem: The user set or uploaded the area of interest and selected the image, taken on July 19, 2019. It’s clearly visible in the screenshot that the individual image fails to cover the area of interest in entirety.
Solution: In this case, the user should select a preview card with an appropriate number of scenes that fully covers their AOI, from the generated search results, and click on the “Mosaic” element.
Conclusion: Mosaic allows for the monitoring of large areas
Before now, monitoring large areas required the user to switch between scenes and merge them manually. This process was rather inconvenient and time-consuming. From now on everything is fast and easy: set your AOI and LandViewer will automatically manage the rest for you.
Use- case 2 - Fire Monitoring in California
Objective: To define the damaged area, that is to apply the NBR index and download the Mosaic scene
Description: In November 2018, a massive fire erupted in California, killing at least 85 people. Almost fourteen-thousand (14,000) homes were destroyed, and approximately one-hundred and fifteen-thousand (115,000) hectares of forest were lost . Local authorities called it the largest fire in state history. This comment comes as no surprise, despite the fact that in the previous year more than one-hundred-thousand (100,000) hectares were also lost.
Local Californian authorities deployed approximately five-thousand firefighters to extinguish the fire, who barely managed to keep up with the fire, which in some areas spread at a speed of 130 kilometers per hour.
Solution: To determine the damage to the affected regions , it is necessary to compare pre- and post-disaster Mosaics with the NBR index applied.
Step 1: Draw or upload your area of interest AOI and set a pre-disaster date
Pre-disaster image 1. The result of rendering a mosaic for the full area of interest (AOI) coverage
Step 2: Select the preview card with the Mosaic, proceed to the “Band combinations” tab, then select the NDR index. At this step the system displays the calculated index values, highlighted in orange-green. Next, continue to the “Download” tab and select the area in which you need the requested pertinent data.
2 image: - The scene with the NBR index displays the situation during the fire.
Step 3: Select the post-disaster image for the same area of interest (AOI)
Pre-disaster image_3. The result of rendering a Mosaic for the full area of interest (AOI)
Step 4: Acquire the Mosaic download results using the NBR index, following the same algorithms found in step 3
Result_image_4 The post-disaster scene shows the affected area and visualizes the damage
Result: The affected areas are shown in red. While comparing the pre- and post-disaster images with the NBR index values, we can assess the damage.
Let Mosaic do the Work for You
In conclusion, Mosaic offers a unique solution to acquire one image that fully covers your area of interest, no matter the size, with the best results. Mosaic allows for a combination of daily satellite images obtained from one sensor for a set location, default or custom indices on-the-fly, and the possibility to download the scenes for further analysis. Say goodbye to manual preselection, image switching, blank spaces, and manual image stitching, forever.
For detailed information on Mosaic, check LandViewer’s user-guide or email us at email@example.com