Author: Jon Coursey
Satellite Imagery is used for a wide range of projects, but
often times it is tough to figure out just which type of data is needed. In the
world of remote sensing, there are many different satellite sensors, all with
different resolutions and multispectral capabilities. In this blog, we will
explore some basics of remote sensing, what all is available, and common
applications of the data.
Remote Sensing 101
As great as a natural color image can look, it is not
collected in the same way as, say, the camera on your iPhone. The process of
collecting imagery is most commonly referred to as remote sensing, which
basically means objects on earth are detected and classified without direct
contact. This blog will focus on passive sensing, as this is what is used for
natural color and multispectral images (except radar). Passive sensors gather information
via radiation that is either emitted or reflected by whatever object the
satellite is trying to capture. This data will be captured with whatever
spectral bands a sensor can acquire (generally red, green, blue, and near
infrared), then sent down to a ground station for processing. From here, the
natural color or multispectral image you might have ordered would be put
A wide variety of sensors and band combinations are
available, and the best options will depend on what you are trying to view, and
the size of your project area. Below are a few situations one might face when
deciding how to go about selecting the most suitable captures.
What kind of imagery do I need for a base map?
This is generally our most common request. Engineering,
architecture, etc. firms will go for images to view ground conditions before
building on their project areas. Essentially, they just need an accurate and
high resolution picture. In these cases, natural color is the best option.
How much resolution do I need?
This will come down to how large your project area might be,
and what is important that you can view with quality. Say your project requires
you to obtain an image of California. For this, you wouldn’t want as high of a
resolution as if you needed an image of, say, an airport. This would be an
extreme amount of detail for such a large area, and would result in enormous
file sizes. Additionally, higher resolution sensors typically capture smaller
area sizes, so many would be required to fill such an area. And if full
coverage even existed, it would be from images accumulated over the course of
many months or years. Lower resolution options will give a better overview of
an area of this size, and generally use less images to complete the coverage.
One great option is to obtain
high resolution imagery of a project site, and lower resolution for the general
area. In the images below you will see captures from both the RapidEye & GeoEye
sensors. RapidEye captures at 5 meter (being the lower resolution), and GeoEye
captures at 0.5 meter resolution. Both show coverage of islands of Hawaii. As
you can see, RapidEye still has great detail for a larger city area, but GeoEye
has the ability to see specific features within such a city.
Figure 1: GeoEye image (0.5 meter
resolution) Figure 2: RapidEye
image (5 meter resolution)
When would I need the multispectral bands?
The most common uses for these are measuring crop health and
doing vegetative analysis. Most sensors available at MapMart will be equipped
with four bands, which are red, green, blue and near-infrared (or RGB &
NIR). An image made from these four bands within the ENVI software environment
is below. For crop health, one would measure relative reflectance along the
wavelengths of these bands. When crops are not healthy, one will notice a
decreased reflectance, mainly in the near-infrared reflectance plateau, but
also with the blue and green regions of the spectrum.
Multispectral bands can also be used to detect different
characteristics on the earth’s surface. Soil, plants, asphalt, etc. all have
different spectral signatures, which would be apparent through these multispectral
bands. Depending on how many bands you have available, and where they are along
the light spectrum, you can start to see more differences within each surface.
For example, an asphalt rooftop may appear as only one color with the standard
RGB & NIR bands available. If you were working with shortwave infrared (or
SWIR) as well, you would start to see different colors within your image. This
is because the differences in the components of asphalt are now being detected.
While many applications of this type of data exist, we have
covered the most common ones we are contacted for at MapMart. Fortunately, with
such a large archive of satellite imagery already existing, with the
opportunity to have more collected, a solution can be found for the most unique
type of geospatial project. If you need data or help figuring out what type to
use for a project, contact us at MapMart.com.
Categories: ENVI Blog | Imagery Speaks
In a blog post I wrote a few months ago, I introduced
the Instant Satellite Imagery Portal section of the Harris Geospatial Marketplace. This
service offers a faster, less expensive alternative to purchasing
DigitalGlobe imagery directly from a sale’s representative. However, at the
time, it could still take up to 48 hours for the image to be delivered
following purchase. This is no longer the case. Thanks to some savvy
engineering by our technical team, the wait time for imagery
download has been reduced to just a few minutes.
Often times, someone will contact us with a request for
imagery, but will have a deadline that would generally be impossible to meet.
And even when ordering directly from a provider, the rush delivery options
could still mean up to a 48 hour delivery time. This service was created with
these types of requests in mind. If someone is new to purchasing imagery, they
may not know the typical delivery times for satellite captures. Additionally,
the need for an image could have been realized towards the very end of a
project, with too little an amount of time to actually receive one. Whatever
the case, our Instant Satellite Imagery Portal hopes to offer a solution for
While in the middle of automating the Portal, it occurred to
our technical team that “hey, this might just work for other products”. This
idea recently came to fruition, with many of our other datasets becoming
immediately downloadable following purchase. Currently, the following products
have been included:
SRTM Elevation Data
NED Elevation Data
Harris Gap Filled Elevation Data
These datasets can be ordered via the same process on the Portal. For our Aerial Imagery and Digital Elevation Model sections, you basically have
access to the immediate download option for anything with a price listed.
Although only a few products have been set up for this
service so far, we are working on making this available for any data that does
not require custom processing. This will make the Harris Geospatial Marketplace one of the
quickest and easiest sources for downloadable data. Vector data and topographic
maps will be available very soon, with hopes of adding more sources for
satellite imagery and elevation data by the end of 2016. For any project facing
a deadline that requires some sort of geospatial data set, the Marketplace will soon be
The Harris Geospatial Marketplace offers a top-of-the-line photogrammetric mapping service called “HiDEM”. This service involves collecting a pair of
stereo images to create high resolution, high-accuracy Digital Elevation Models
(DEMs). A team of experts with more than
25 years of photogrammetric mapping experience work behind the scenes on HiDEM
to deliver the best surface and terrain models in the industry.
Figure 1 Overhead View of HiDEM Data
1 meter Digital Surface Model (DSM) data
5 meter Digital Terrain Model (DTM) data
1 or 2 meter Contour data (1m contours displayed
in above image)
0.5 meter Natural Color Ortho Image data
Highly accurate at sub-meter RMSE vertical using client-supplied ground survey control points (GCPs
Source Imagery: Pleiades-1, WorldView-2, WorldView-3 WorldView-1, & GeoEye
Why Use HiDEM?
HiDEM custom tasking is the perfect service if you need high
resolution and highly accurate elevation data for a project site. Below are a
few examples of how customers are using this data:
How It’s Done
Because end users will often have trouble sending a land
survey to his or her project area (due to large area size, difficulty accessing
the area, etc.), remote sensing is used. In this case, stereoscopic satellite pairs
are collected. With our HiDEM service, the points of objects on the ground are
determined by our photogrammetric team from the pair of images. Lines of sight
are constructed by finding the same points between the images, then determining
the three dimensional location of each through the intersections of these
lines. While the creation of the elevation model through satellite mapping is
similar across the imagery, there are processes and algorithms used by our
production team that make Harris Geospatial process unique.
The Harris Geospatial
While many companies create elevation models with comparable
resolutions, our hands-on approach delivers a more refined, better –quality end
product. Our photogrammetrists take the time to look over each model of a
project area to account for details that may have been missed. For example,
with a 5 meter resolution terrain model, a pipeline in a project area that is
say 4 meters in width would not show up in the raster image. A member of our
team would identify this detail and add break lines around the pipeline to
account for it. Many of our competitors generate terrain models automatically
which would miss key details like this one and create the potential for costly
problems down the road.
Additionally, our team will work with you throughout the
project to make sure nothing is overlooked at any point along the way. A project
manager will assist you in selection of ground control points (GCPs), defining
area boundaries, and identifying other details that need to be addressed. As a distributor
for all the leading satellite imagery providers with access to a large
constellation of sensors, we can facilitate getting your job done quickly and
efficiently, both in terms of time and money. Furthermore, with a large archive
catalog to choose from, we can find the best stereo pair imagery and deliver it
to you faster than a company who only works with their own satellites. All of these
factors mean that Geospatial Marketplace customers get the best elevation
models within the shortest time frame for the best value – hands down. Not a
customer yet? Talk to us to see how the HiDEM service can work for you.
The Instant Satellite Imagery Portal is a new, easy to use,
DigitalGlobe imagery ordering system offered exclusively through the Harrisgeospatial.com/marketplace.
Using the “clip and ship” method, customers can purchase high resolution,
natural color imagery of his or her area of interest, and receive the data
within hours. These captures come standard as orthorectified, with little to no
cloud cover present. On top of a large archive to choose from, the Imagery Portal
offers the following benefits:
The imagery offered through this
service is a great option for multiple types of projects. Whether you just need
a picture of your house, or base map data for site building plans, you can find
imagery here that can fit any budget.
How to Order
You can find and purchase the Satellite Imagery Portal data through a number of ways on our website. Once you have gone to
Harrisgeospatial.com/marketplace, a banner will appear at the top, such as is seen in the image
below. From here, you can either click the big red button in the middle reading
“Download Current Satellite Imagery Right Now”, or click “Data Store”, which is
highlighted in the tool bar at the top. If you click the “Data Store” link, you
can proceed by clicking the “Satellite Imagery Now” option.
From here, you will be taken to the section where you would
define your area of interest. This can be done a number of ways. In the image
below, you will see where you can type in an identifier of your area
(coordinates, address, city, etc.), and the tool bar which allows you to create
a polygon around your area. These have both been circled. Through the
“Utilities” section on the left side of the page, you can upload a KMZ or SHP
file of your area as well.
Once your area has been defined, you will then be taken to
the checkout page. The Imagery Portal data will be presented with the title
“DigitalGlobe Satellite Imagery”, as seen below. From here you can see the
price, capture date, resolution, and the amount of coverage of your area
provided by each image. By clicking the “View” button, you see a low resolution
sample showing the coverage. While the quality will be much lower than the
image you would receive, it will be enough to show if there is any cloud cover
over your area.
After finding the image best suited for your
project, all that’s left is filling out your contact information and credit
card number. With very few exceptions, this data is accessible to anyone in
almost every country. A group of sales persons and customer services
representatives are also available if you have any questions regarding the
imagery before committing to purchase.
Our goal with the Instant Satellite Imagery Portal is to offer
the most affordable imagery of the highest resolution for as much of the world
as possible. We often see requests of persons just wanting a picture of his or
her house or neighborhood, and don’t have the want or the budget to pay for 25
square kilometers of imagery. This option also makes it more feasible for
larger projects from, say, civil engineering or oil and gas firms. It is not
uncommon for us to receive requests from such companies needing a base map
image before working on a site, but will realize that the preexisting budget
for the project did not account for such a high minimum area. Instead of having
to opt for a lower resolution, older capture, they could now find an image at
the desired resolution for a much lower cost. Even for larger scale projects,
this service makes high resolution imagery more accessible and less expensive
than it was before.
Tags: DigitalGlobe, Data Store, Marketplace, Mapmart, download high-res imagery, Instant Satellite imagery
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