Lesson 11F: New elevation products and services from 3DEP lidar data

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This is lesson 11f. In this lesson, you will learn about the new lidar products available through the 3D Elevation Program 
 

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Date Taken:

Length: 00:21:15

Location Taken: Augusta, ME, US

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In this lesson, you will learn about the new lidar products available through the 3D Elevation Program (which is abbreviated as “3DEP”).

The lesson will introduce the 3DEP program, discuss the lidar data available, and where to find the data.

USGS has a long history of providing elevation data, first through contours on topographic maps and later as digital files in the National Elevation Dataset.

The 3D Elevation Program is our newest effort to provide national elevation data.

The program applies ground-breaking lidar technology to generate not only a much higher resolution bare earth elevation surface, but it also provides us with 3-dimensional data of all the natural and manmade features.  These data are transforming industries and creating new applications never before possible.

The program also calls for increasing the quality level of lidar data being acquired because it meets more mission critical applications.  Our goal is to acquire national lidar coverage in eight years, with ifsar data in Alaska.

The applications highlighted on this page represent uses of elevation data applied within each of the USGS science mission areas.

USGS is not alone is our widespread use of the data.  Other agencies contributing funding to the program have similarly discovered the value of the data and are experiencing a high return on investment for the dollars they commit to the program.

3DEP is a collective effort to develop partnerships to fund the program and accelerate the rate of acquisition to enable these benefits on a national level.

The 3DEP program is based on the results of the National Enhanced Elevation Assessment (called “NEEA”).  NEEA documented the elevation data needs of users across the country.  The full report is available on the USGS National Map website.

NEEA proposed several different “Quality Levels” of elevation data with varying data resolution, accuracy, and costs.   QL1 represented the highest quality product whereas QL5 was the lowest.

A cost benefit analysis was performed to determine the elevation products best meeting user needs.   A number of scenarios were developed and one meeting the most needs at a reasonable cost and timeframe was chosen.

The preferred scenario recommended QL5 data for Alaska and QL2 (or better) for the other 49 states and the US territories.

The goal of the 3DEP program is to generate a new topographic base layer for the United States and its territories.  For the continental United States, Hawaii, and US territories, airborne lidar sensors will be used to gather elevation data.  For Alaska, slightly lower resolution airborne radar-based ifsar sensors will be used.

Both sensors can generate a dense collection of point features.  These points have an X and Y positional location and a Z-value for height.  The points depict the all the surfaces detected by the lidar and ifsar sensors.   These points reveal ground terrain (called bare earth) as well as features above the ground such as structures and vegetation.  This image shows individual elevation points representing the ground surface in the bottom frame.  The middle frame shows the ground points joined in a triangulated irregular network, or TIN.  The top frame shows a solid bare earth ground surface built from the lidar point collection.

A number of data products are generated from the lidar and ifsar input.  This table lists the different products available through 3DEP.   One of the key derived products is the Digital Elevation Model (or DEM) which are 3D representations of the bare earth surface.  DEM surfaces are formed by a grid of square cells, each cell having one elevation value.  DEM resolution varies by cell size, with smaller cells capable of showing greater terrain detail.  USGS has been producing DEM data for many years; the difference with the 3DEP program is that the DEMs are newer and have a higher resolution.

Seamless DEMs are designed to provide uniform and complete elevation data across a large region.

Project Based DEMs have higher resolutions than the seamless DEMs and are delivered as individual lidar projects are completed.

Source Data refers to products other than the familiar DEMs.

Before we look at the next slides which provide details on each group of elevation products, note that the one and five meter project based DEMs and all the source data products were new to The National Map starting in 2015.

The seamless DEMs are designed to provide uniform and complete elevation data across a large region.  Note that the 2 arc-second DEM is for Alaska only.  The 1 arc second DEM is even available across Canada and Mexico, although the non-U.S. DEMs are not being currently updated.

The highlights listed here provide the basic data characteristics.  Seamless DEMs are always bare earth and do not include above grade features.  “Hydroflattened” refers to a consistent elevation built in along the edges of waterbodies and large rivers so that the water forms a smooth surface.

The seamless DEMs are also distributed by large one degree blocks, simplifying the distribution process.

1/3 arc second (or ten meter resolution) and 1 arc second (30 meter resolution) DEM data have been around since long before 3DEP.  The original DEMs were based on the original topographic map contours lines so their data sources are older.  The 1/3 and 1 arc second DEMs are being replaced by newer versions based on lidar as it becomes available.

These next images illustrate the differences in the seamless DEM resolutions.

This image shows a 2 arc second DEM with its 60 meter resolution.  This is showing a coastal region in Alaska.

This is the same region now showing the 1 arc second seamless DEM with a 30 meter resolution.

Finally, this is the same region with a 1/3 arc second DEM with a higher ten meter resolution.  Note that the image scale has remained the same but greater surface feature detail is visible as the resolution improves.

This graphic shows the distribution of the seamless DEM products.

The 1/3 arc second product is seamless across the continental U.S. plus Hawaii and the territories.  The 1 arc second DEM also has the same extent plus it adds Canada and Mexico.

The 2 arc second DEM product covers Alaska.  More of Alaska is being covered by the 1 arc second and 1/3 arc second DEMs but the state will continue to be covered by 2 arc second product.  

The project based DEMs are provided and made available as individual lidar projects are completed and approved.  These are typically higher resolution DEMs and are not merged together to form a seamless product.  These higher resolution DEMs are used, however, as input to update the 2, 1, and 1/3 arc-second seamless layers. 

One meter DEMs have become a standard lidar deliverable and are now being provided rather than the 1/9 arc second DEM.

There are three resolutions of project based DEMs.  The following slides show some of the differences between them.

The 1/9 arc-second DEM specifications are listed here.  Until 2015, the 1/9 arc-second DEMs were the highest resolution DEM distributed online by USGS.  1/9 arc-second is approximately a three meter grid cell.

The one meter DEM is a common deliverable in modern lidar production.  Lidar meeting USGS production specifications collect enough data to support a one meter DEM.  Occasionally, lidar projects may provide a higher resolution DEM but a one meter DEM is always generated now for distribution by USGS.   The parameters listed here are common to one meter 3DEP DEMs. 

This image shows a one meter bare earth digital elevation model near the eastern tip of Long Island, at Montauk, New York.

The collection of elevation products for Alaska is different because the data are collected with a radar-based ifsar sensor.

These products have slightly less resolution than lidar-based products but are still far better than elevation data historically available for Alaska.

A major Alaska elevation product is the five meter resolution digital elevation model.   Like other DEM products, it shows the earth’s surface without vegetation or structures.  The basic product parameters are listed here.  Similar to other USGS DEM products, the data are delivered by large one degree blocks, which makes staging and delivering data easier.

This image shows the five meter Alaska project based DEM for the Mount Edgecumbe area near Sitka, Alaska.  Landforms are clearly visible.

We have covered the seamless and project-based DEM datasets.  Source data are other related data available for download.

Source DEMs are shared with USGS from another organization, and have different characteristics from 3DEP products.

A digital surface model (or DSM) is similar to a DEM but it also includes above ground features such as buildings and vegetation where present.  This product is available in Alaska only.  The orthorectified radar intensity imagery is an ifsar product and is also only for Alaska. 

The lidar point cloud is the original collection of X, Y, and Z points gathered by the lidar sensor and is a required deliverable.  There is no point cloud product from the ifsar sensor for Alaska. 

We will now take a closer look at these four Source Data products.

Original Product Resolution (OPR) DEMs are different from the standard 3DEP DEM products.

Lidar projects sometimes generate DEMs that differ from standard USGS products.  This may mean different projections, resolution, format, or hydrography treatment (such as a hydro enforced DEM).  The OPR DEMs had previously been distributed as a seamless product covering the entire project, but USGS will soon deliver the OPR DEMs based on their original tiled grid.

OPR DEMs may be provided in addition to the usual seamless and project based DEMs.

The National Map Viewer can show how the OPR DEMs fit in with the other DEM products.

Clicking on the 1 arc-second DEM, this seamless product covers the entire area, including Mexico.

Clicking on the 1/3 arc-second DEM, this other seamless product covers a large extent but does not go far into Mexico.

Clicking on the 1 Meter DEM shows the higher resolution project based DEM for a coastal San Diego project obtained in late 2014. 

Clicking on the DEM Source (OPR) also shows data covering the San Diego project area.  The footprint looks similar to the 1 meter DEM but this is a different dataset.  The original DEM data differ in using a state plane coordinate system and having a 2.5 foot resolution, so these are included as an OPR dataset.

The digital surface model (or DSM) shows all features initially recorded by the radar sensor, such as buildings and vegetation.  The DSM is only available for Alaska.  Since it comes from the ifsar sensor, it also has a five meter resolution like the Alaska DEM.  Some of the DSM characteristics are shown here.

Here is an example of the Alaska digital surface model.  This shows a portion of northern Anchorage with mountains to the east of the city.  A digital surface model shows surface detail initially captured by the elevation sensor, so buildings and vegetation are shown. 

Another source data product which is available only for Alaska is the radar intensity image.  These are orthorectified images that have the appearance of a black and white aerial photograph.  Some of the intensity image characteristics are shown here.

This orthorectified raster intensity (ORI) image shows a region centered on the University of Alaska in Anchorage.  The gray tones are based on the intensity of the radar return; dark areas are more indicative of smooth surfaces such as paved roads or water.  Rougher surfaces scatter the radar pulse and can create brighter returns.  The brightest returns are often caused by manmade objects (such as the sides of buildings) that can reflect the radar pulse back at the sensor.

The lidar point cloud is the primary source data collected by the lidar sensor.  All other lidar products (such as contour lines or a DEM) are derived from these points.  Each point has its own X and Y coordinate for location plus a Z value for height.  Points clouds are often dense collections of points, with multiple points per square meter, depending on the quality level.  Points are typically assigned a classification by the surface they represent, such as bare ground or water.

Point clouds are comprised of individual points gathered by the airborne lidar sensor.  This image  shows the points making up the Golden Gate Bridge and the headlands at either end.  Points are colored by height with the higher points in red.  Although this has the appearance of a continuous ground surface, the image is made of separate points.

The 3DEP metadata page listed here has details on the metadata available.  Metadata is available in two varieties: textual metadata and spatial metadata

Textual metadata is provided with the 3DEP data download.  Typically there will be an XML file containing metadata for the source of the dataset you download.

Depending on the data site you are accessing, some of the metadata may be visible when clicking on a metadata link or icon.  This image shows the downloadable material on The National Map viewer site for a DEM dataset.  The arrows point to viewable metadata; the metadata is also included should you download the dataset. 

Spatial metadata provides details on a specific elevation product (such as a seamless DEM).  This metadata is provided as a shapefile with information provided for all polygons.  This image shows one third arc-second DEMs in the San Diego area.  The different polygons are related to the origin of the data.  Identifying a polygon provides details on the elevation data, including its source.   The website has a 3DEP data dictionary with details on the codes in the attribution.

Most National Map digital products are typically accessed either by viewing the data through an online mapping service or by downloading the actual data files.  3DEP elevation data can be accessed through both methods.

Online map services allow you to view data in your GIS software (such as ArcMap or Global Mapper) or on map viewer websites without needing to download data files.

The alternative is to download the data files and view them using GIS software. 

USGS also has an elevation point query service, where the seamless DEM will provide an elevation value at a given coordinate.  The URL for this service is shown on the upcoming links page.

USGS has a list of map services providing data from The National Map.  The service list link is shown here. 

There are several map services showing products derived from 3DEP data.  They include a shaded relief, contour lines, and data availability.

This image, for example, shows the USGS shaded relief and contour line map services turned on within ArcMap software over San Diego County.  No data files were downloaded to view the data.  The map services are simply turned on.  Since the data are being viewed in a GIS, you could also bring in additional local data which can be displayed along with the 3DEP products.

Lesson 5, in this series of modules, provides further instructions on how to use The National Map web services in ArcMap.

Sometimes it’s preferable to download the data files.  This is especially true, for example, if you need to manipulate or analyze the data content.

3DEP data can be downloaded from a number of source sites.  This list provides the site names and links.  The first site listed, The National Map Download Client, is the primary repository for digital USGS mapping data.  Lesson 4, in this instructional series, provides further details on using the Download Client. 

In this lesson, you learned about elevation products and map services offered through the 3D Elevation Program.

Current information on the 3DEP program can always be found on the National Map homepage shown here.