5

Oct

2016

Choosing the right type of imagery for your project

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 together.

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.

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Categories: ENVI Blog | Imagery Speaks

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6

Jul

2016

Ordering from the Marketplace Just Got Better

Author: Jon Coursey

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 such issues.

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:

-          NAIP Imagery

-          CityOrtho Imagery

-          GeoOrtho Imagery

-          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 solution.

 

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Categories: ENVI Blog | Imagery Speaks

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17

May

2016

High-Resolution, High-Accuracy Topographic Mapping Services

Author: Jon Coursey

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

Project Deliverables

  • Key Deliverables:
      • 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:

  • Drainage and hydraulic projects, such as mapping out sites to build a dam
  • Mapping out sites before building a mine
  • Mapping the area along pipelines for oil and gas industry

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 Marketplace Advantage

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.

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Categories: ENVI Blog | Imagery Speaks

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11

Apr

2016

New service to immediately download 50cm+ Imagery

Author: Jon Coursey

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:

  • Delivery within a few hours (compared to multiple days), with no added rush order costs
  • Lower square kilometer rate
  • 10 square kilometer minimum area required for purchase, 15 square kilometers smaller than the industry standard
  • Coverage of nearly the entire world

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.

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