Data Picking Tutorial

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User guide-Developer Guide

The updated imb.picker works with layer information that has been loaded into ops.cresis.ku.edu and stored in layer data files. Maps can be loaded from the OPS geoserver and Google. Flight lines can be loaded from season layer files (csarp_support/layer/) or from the OPS geoserver which loads them from the OPS database. Two way travel times can be loaded from layer data files or from OPS Django which loads them from the OPS database. To make changes to the two way travel times stored in OPS (ops.cresis.ku.edu) as opposed to just browsing, you must be working from a KU or IU-Bloomington computer and have an OPS account; email cresis_data@cresis.ku.edu if you do not have an OPS account or your computer still cannot do layer edits from these computers. You can also follow the instructions to setup your own OPS server and point to this instead to be able to do edits.

Contents

What is "The Picker"?

The Picker or image browser is a custom MATLAB GUI for digitizing layers from radioechograms. This guide details all of the various features of the tool, fundamentals of interpreting radar depth sounder echograms, and fundamentals of digitizing layers using the tool. All first-time users should read through and complete this tutorial.

Setting up MATLAB

There are a few things you will need to do before you can run the picker tool.

CReSIS Toolbox Setup

Complete setup steps here. The picker can be run on any Matlab platform (Linux, Windows, and Mac). Matlab's GUI tends to have fewer problems on Windows than on Linux.

OPS Command Setup

In MATLAB type:

edit opsCmd.m

Make sure that the following variables match the following values:

gOps.profileCmd = false;
gOps.sysUrl = 'https://ops.cresis.ku.edu/';

Using the Picker

To start the picking in MATLAB simply enter:

imb.picker

Two windows will open, the map, and the preference window. A login window will also open if you connect to OPS. You need to obtain a login from the OPS server administrator if you want to be able to modify anything otherwise use "anonymous" and "anonymous" for the username and password respectively. Multiple instances of the picker may be run at the same time from the same Matlab session although it is generally better to run them from different Matlab sessions to obtain a better software response time.

Preference Window

The first window you need to interact with is the preference window. It allows you to select what information you will be viewing in the map window and later on in the pick windows. Preference Window
To set up the preference window follow these steps:

  1. Select the layer source. The options are:
    • OPS for the Open Polar Server geospatial database which needs to be specified in opsCmd. Choose "Connect to OPS" if the imb.picker has not connected to OPS yet.
    • layerData files stored in your gRadar.out_path
  2. Select the layer data source if the "layerdata" layer source is chosen. This is the file path to use for layer data. This is always relative to the season's out_path directory and "CSARP_" prefix is always added to the folder name. Therefore, to use "CSARP_layerData", just enter "layerData". If you need to add a path that is not shown, right click and choose "add" or "edit".
  3. Select the layers to view if using the OPS layer source. Select these from the available layers box (double click to select or select all that you need and then right click and add)
    • You must select standard:surface at least or echograms will not load. Normally standard:bottom is also selected for picking.
  4. Select the sensor (radar) from the available sensors box with a single click
  5. Select the seasons you wish to load from the "available seasons" box by either double clicking or select all that you need and then right click and add.
  6. Select a map from the Available Maps box. The maps that are not "blank" or "google" are populated from the OPS Geoserver and you have to choose "Connect to OPS" the first time.
    • arctic:Greenland Mapping project_2000_15m: The best for Greenland
    • arctic:arctic_natural_90m: The best for parts of Canada
    • arctic:arctic_naturalearth or arctic:google: The best for all other arctic locations
    • antarctic:Antarctica_LIMA_15m: The best for West Antarctica
    • antarctic:Antarctica_LIMA2: The best for East Antarctica
  7. Add/remove echogram sources by right clicking and choosing add source.
    • Normally, should add: "CSARP_post/standard", "CSARP_post/mvdr", "CSARP_post/qlook", "standard", "mvdr", and "qlook".
  8. Select the flightline mode.
    • If using OPS layer source, then "OPS flightlines" is the best for routine picking. The other modes provide additional information (e.g. colorcode flightlines based on quality level or ice thickness), but are much slower to draw. If using
    • If using layerdata layer source, then you need to run imb.create_season_layerdata_files for your season if it has not been done already and then choose "layerdata flightlines".
  9. Click OK to load your selection

Available Sensors

When "layerdata Flightlines" is chosen, this listbox only shows "layerdata" since all sensors can be viewed at once in layerdata mode. When "OPS Flightlines" are chosen, this listbox shows the sensors that are stored inside of the OpenPolarServer database (the picker automatically connects and retrieves this information). Only one sensor type may be viewed at a time in OPS flightlines mode. For example, the "rds" sensor type represents all of the depth sounding radars (icards,acords,mcrds,mcords,mcords2,...). Each season of data is categorized into one of the four categories: "accum", "kuband", "rds", and "snow".

Available Seasons

If OPS flightlines are chosen, this listbox shows the seasons that are stored inside of the OpenPolarServer database based on the selected sensor.

If layerdata flightlines are chosen, this listbox shows the season layerdata files that are available in the csarp_support/layer folder. These files are created using imb.create_season_layerdata_files.m. This script concatenates all the layerData file for each season into a single file to allow for faster loading. Note that the sensor type ("accum", "kuband", "rds", and "snow") is also shown with the season name (YYYY_LOCATION_PLATFORM) since you can choose multiple sensor types to display at the same time.

From this listbox you can select the seasons you wish to view in the map. You can select seasons two ways:

  1. Double-Click on the season in the "Available Seasons" window and it will move to "Selected Seasons"
  2. Single-Click on the season in the "Available Seasons" window, click the "Add -->" button and it will move to "Selected Seasons"

Selected Seasons

This listbox shows the seasons that you have selected to load into the map. To remove seasons from this lists you can:

  1. Double-Click on the season in the "Selected Seasons" window and it will move to "Available Seasons"
  2. Single-Click on the season in the "Selected Seasons" window, click the "Remove <--" button and it will move to "Available Seasons"

Selected Images

This listbox shows the images (also known as echograms) that the picker will search for when loading an image into the echogram window. The defaults are "CSARP_post/standard", "CSARP_post/mvdr", "CSARP_post/qlook", "standard", "mvdr", and "qlook" unless you remove them. You can add or remove echogram sources by doing the following:

To add an image source:
  1. Right-Click in the "Available Images" window and select "Add"
  2. Type the name of the source (e.g. "standard" for "gRadar.out_path/RADAR_NAME/SEASON_NAME/CSARP_standard" or "CSARP_post/standard" for "gRadar.out_path/RADAR_NAME/SEASON_NAME/CSARP_post/CSARP_standard"). The paths are always relative to the season's folder in gRadar.out_path. The "CSARP_" prefix is always added to the last folder name.
  3. Click "OK" and the source will be added
To remove an image source:
  1. Single-Click to the select the source in "Available Images" and Right-Click on it.
  2. Select "Remove" and the source will be removed

Available Maps

This window shows the background (reference) maps available from the OpenPolarServer map server and always shows blank and Google map options as well. The selected image will display behind the flightlines in the map window. The quickest option is the "Coastline" map but the imagery options will be more valuable for reference. You can change the background map at any time while using the picker so you are not stuck with your first choice. Select the image by using the drop-down menu.

Map Window

After clicking "OK" in the preference window the map window will refresh and display the information you selected. At this point you can close the preference window if you would like. All your settings are saved and the window can be re-opened at any time by clicking "Prefs" at the top of the map window. Press F1 to print out a list of commands to the console.

Map labeled.png

The map window is the "control" of the picker. It allows you to select data to load in the pick windows and more. Here is an explanation of the components of the map window:

Search Box

Allows you to search for specific data using the search box at the top left. The search window accepts the following inputs:

  • YYYYMMDD (Year Month Day)
  • YYYYMMDD_SS (Year Month Day Segment)
  • YYYYMMDD_SS_FFF (Year Month Day Segment Frame)

Window Selector

Allows you to select a pick window to load data into (or a new window). This version of the picker allows you to open multiple pick windows at the same time.

Load Button

Loads the selected frame into either a new or current pick window (based in the window selector).

Zoom Controls

There are multiple ways to zoom in the map window:

  • With the focus on the window (click the outer box of the window) click "z" until the zoom cursor appears. You can now draw a box (left-click and hold) around the area you want to zoom on. You can also just single left-click to zoom to a spot Give the map a few seconds to refresh.
  • You can also use the scroll wheel on your mouse to zoom in and out (this is a bit laggy so be careful)
  • To zoom out to the full extent use the zoom cursor (press "z") and then double-click with the right button on your mouse.

To pan in the map window use the arrow keys on your keyboard.

Selection Controls

There are multiple ways to select a flightline to load in a pick window (make sure the zoom tool is off "z"):

  • Hold CTRL and left click near the line you wish to select
  • Use the search box to select a specific line

Note: To directly select and load a frame you can double left-click anywhere in the map. It will select and load in a new or current pick window (based on the window selector) the closed frame to your double left-click in the map.

Pick Window

After loading a frame from the map window a pick window will open. From here you will digitize and modify existing and new layers on radar echogram images. The pick window offers a suite of tools to make this process as easy as possible.

Pick labeled.png Press F1 to see a list of hot-keys and shortcuts!

Tool Selector

Selects the tool you will be using to digitize the layers on the image. Note that when the echogram window is first opened you will be in zoom mode and cannot use the tools. Press 'z' to toggle between Tracker Mode and Zoom Mode.

(i) interpolate

This tool should only be used if snake or viterbi do not work.

To enter a manual point, left click where you want the point to be. To interpolate between manually entered points, hold ALT and draw a box around the points to interpolate. To delete a point hold the right button on your mouse and draw a box. The tool params "Max point range" sets the search range when entering manual points.

There are two supported interpolation methods. The default is "linear" which connects each ground truth point with lines. The other method is "spline" which uses the smoother "spline" algorithm to connect the ground truth points. Spline has some desirable properties such as continuous first and second derivatives.

(q) quality

Using ALT and drawing a box sets the quality of points inside the box to the value in the quality selector.

(s) snake

The snake tool or the viterbi tool should always be used first if the layer is clear enough to allow the tool to be used.

To enter a manual point, left click where you want the point to be. To snake between manually entered points, hold ALT and draw a box around the points to snake between. To delete a point hold the right button on your mouse and draw a box. The tool params "Max point range" sets the search range when entering manual points. The "Snake range" setting controls how many range bins (i.e. rows of the image) up/down the layer can jump from range line (column of the image) to range line. The snake works outward from every manually entered point and jumps to the largest intensity within "Snake range" bins to the current pixel. Large values of snake range will allow the layer to go up and down rapidly over a short span. Small values of snake range are good for tracking smooth layers.

(b) browse

Not often used. Useful for exploring data without making any changes by clicking.

(c) copy

Copies one layer to another. The tool also supports a number of other operations such as shifting layers up and down, applying differences between layers to other layers, and manipulating layers when copying (any Matlab expression may be used to manipulate the values).

To move layers up and down, select the layers that you want to move up and down and then click on the "Up" and "Down" buttons in the Tool Params window.

To copy one layer to another, select the layer that you want to copy into. Then open the Tool Params window and set the "Source layer" to be the layer that you are copying from. This should be a positive integer that matches the layer number in the layer listbox. For a simple copy, make sure "s=s" in "Source eval". Other types of copying are possible. For example, to copy the double of the layer then set "Source eval" to "s=2*s". Finally, hold down ALT while doing a left click and drag over the layer your are copying from.

To apply the difference between two layers to another layer, check the "Enable Diff" checkbox and set the "Correct layer" to be the layer that is correct. Set the "Source layer" to be the layer that has errors in it. Then when the source layer is selected, all active layers will be updated with the difference "Correct layer" - "Source layer". Note "Source eval" also operates on the difference, but for this operation, most of the time "s=s" makes the most sense.

(v) viterbi

This tool uses the Viterbi algorithm for 2D tracking of layers. Unlike the snake and interp tools, manual (ground truth) points are not required but they are used if available. The function returns a continuous layer for the region selected. To enter a ground truth point use left click. To run the algorithm hold ALT and draw a box around the points. To delete a point hold the right button on your mouse and draw a box.

Tool Params

A dialog that allows you to set values for any of the above tools. Especially important for snake and convert.

Quality Selector

Sets the quality value for entered points, or for use by the quality tool. Default is "Good".

Image Processing

Example of Image Params settings.

This opens the "Image Params" window. Features:

  • Turn the autoscale color axis on/off and manually set the color axis or distort the histogram.
  • Turn on image smoothing/filtering. No filtering is "10*log10(X)" which justs takes the log of the intensity values. Typical is to use the third option "10*log10(filter2(ones(round(param1 ..." which low pass filters the image in the range bin (param1) and along-track (param2) dimensions. You can add your own function to the list where the variable "X" is the intensity, and param1/param2 are controlled by the sliding bars.
  • Turn on noise estimation/detrending. This estimates the noise and then subtracts the estimate before displaying.

The most common setting is shown in the thumbnail to the right.

X Axis

Sets the scale for the x axis. "Range line" is the default and is the relative column number in the image. "Range line" view is usually the best view for tracking layers since it does not require any resampling and therefore should be the fastest to display. "GPS time" is in ANSI-C format (seconds since Jan 1, 1970). "Along track" is in kilometers along-track.

Y Axis

Sets the scale for the y axis. The default/native format is "TWTT" and will be the fastest since no conversions need to be done. The "Range Bin" axis is also very fast since this is just the row number.

"WGS84" is useful for interpreting radar depth sounder data around the ice sheet margins since lakes and the ocean will be flat and the ocean will be near sea level. It assumes that all pixels below the surface are in ice and the TWTT to elevation conversion includes a sqrt(3.15) factor. The "Range" axis converts TWTT to range and includes the ice dielectric conversion as well, but everything is done relative to the radar.

The "Surface Flat" option is best for tracking Snow Radar and Radar Depth Sounder layers since it resamples the image so that the surface is flat which tends to reduce the layer undulations and make them easier to track. Currently it only flattens the image relative to the surface layer, but we plan to implement a version which can flatten all tracked layers.

Frame Count

Sets the number of frames that can be loaded at the same time. 2 is default (dont go below this) and 4 is a safe maximum. Keep in mind you will have to some more than normal with more than 2 frames loaded and some features can appear stretched if not zoomed correctly.

Scale Control

Turns the auto-scaling feature on or off. This should almost never be turned off as it controls the dynamic contrast adjustment as you zoom in and out of the echogram.

Layer Controls

Checkbox turns the layers on and off (visibility) and the button (circle) sets the active layer. You can use the number to set the active layer as well. (Pressing 1 sets the surface as the active layer). You can create or delete layers using this dialog. Delete does not actually delete any data, rather it's sets the layers status to deleted for further review. Hitting "a" selects the Surface + Bottom ground for picking exposed rock/water. You can also select surface + bottom manually by selecting both layers.

Available Frames

A list of the frames available for the segment selected in the map window.

Available Images

A list of the images available for the segment selected in the map window and the sources set in the preference window.

Pick Window

All entry and manipulation of data happens within this frame of the pick window.

Clipboard Functions

In the echogram or "pick" window, you can copy the:

  1. frame ID by right clicking on the frame listbox in the left panel and choosing "Copy"
  2. status text (e.g. for the cursor readout) by right clicking on the status text box and choosing "Copy cursor info" or pressing "Ctrl-C"

In the map window, you can copy the:

  1. frame ID by right clicking on the title of the map and choosing "Copy"

Cursor

To place a cursor on the echogram or map, hold down shift and then click where you would like the cursor to show up. The cursors for each echogram will then update to the closest location that each echogram gets to the location of the cursor that you have just placed. Each echogram has one cursor and this is displayed as a vertical dashed line in each echogram window and as an "X" on the map for each echogram flightline.

Saving and Loading Layer Data

The layer information (two way travel times) may be loaded and saved from either the Open Polar Server or from layerdata files. Once you have used imb.picker to save layer tracking information in one of these two spots, you may use other tools to load and view the layer information. A list of these tools is provided in the CReSIS Toolbox Guide.

Using the Slice Browser

The slice browser is for browsing and tracking layers in 3D imagery (layers stored in surfdata files). The slice browser cannot be used with 2D images.

The imb.slice_browser is not integrated with the imb.picker, but we plan to do this for the v3.2 release in June 2021. For now, imb.run_slice_browser is the script that shows how to call imb.slice_browser.

Each primary surface may have the following surfaces:

Surface Description
Active Active surface. This is where the final two way travel time information is stored for the surface in question. This layer can only be changed by running the tracking algorithm. It cannot be modified directly.
Ground Truth Ground truth surface. This is where user supplied data points are stored for the active surface. This surface may be modified by deleting ground truth points and adding ground truth points. This is used to aid the tracking algorithm.
Mask Binary ice mask. If true, then the surface at this point may take on a value that is different than the air-ice surface. This is used to aid the tracking algorithm.
Quality Binary quality mask. If true, then the surface at this point will be used in generated data products otherwise the corresponding two way travel time in the active surface will not be used.
Surface Two way travel time to the air-ice surface. This is used to aid the tracking algorithm.

The tools that can be applied are:

Function m-file Description
TRW-S imb.slicetool_trws.m Applies tree reweighted sequential based tracker to track a surface. Uses the ground truth, ice surface, and ice mask surfaces to output to the currently active surface.
Delete imb.slicetool_delete.m Deleting ground truth from the active layer's ground truth surface. Left click and drag in surface view applies delete to the selected region.
Quality imb.slicetool_quality.m Set the quality for the active layer's quality surface (binary mask). Left click and drag in surface view sets the quality to zero (bad quality) in the selected region. Holding down shift when releasing the mouse button sets the quality to one (good quality) in the selected region.

Slice Browser Window

Action Description
Arrow keys Pan view in the direction of the arrow key
Double click Zoom: Zooms to full dataset (similar to a "home" function).

Tool: sets the ground truth to where the click was done

F1 Prints help message with all keyboard shortcuts to console.
Mouse motion Moves the cursors around in the surface and echogram windows to show where they intersect with the current mouse position.
Left click Zoom: zooms in at the selected point

Tool: sets the ground truth to where the click was done

Left click and drag Zoom: zooms to the selected region

Tool: sets the ground truth to where the click was done

Right click Zoom: zooms out at the selected point

Tool: Toggles state of selection for the selected column.

Right click and drag Zoom: zooms out at the selected point

Tool: Select layer points which controls which elevation bins will be operated on.

'r' Redo the most recent command that has been popped from the undo stack. I.e. this is the inverse of the "u" command.
'u' Undo the last command that could affect a surface.
'ctrl-z' Zooms to full dataset (similar to a "home" function).
'z' Enter zoom mode

Surface Window

Action Description
Arrow keys Pan view in the direction of the arrow key
Double click Zoom: Zooms to full dataset (similar to a "home" function).

Tool: Changes the slice view to the slice where the double click was done.

F1 Prints help message with all keyboard shortcuts to console.
Mouse motion None
Left click Zoom: zooms in at the selected point

Tool: Jumps the slice window to the selected slice

Left click and drag Zoom: zooms to the selected region

Tool: Selects which elevation bins will be operated on

Right click Zoom: zooms out at the selected point

Tool: Jumps the slice window to the selected slice

Right click and drag Zoom: zooms out at the selected point

Tool: Apply a tool to the selected region. Modifier keys (alt, shift, ctrl) may affect how the tool is applied. For example, holding shift when creating the drag box with the quality tool sets the quality to good where as without shift it sets the quality to bad.

'ctrl-z' Zooms to full dataset (similar to a "home" function).
'z' Enter zoom mode

Echogram Window

Action Description
Arrow keys Pan view in the direction of the arrow key
Double click Zoom: Zooms to full dataset (similar to a "home" function).

Tool: Changes the slice view to the slice where the double click was done.

F1 Prints help message with all keyboard shortcuts to console.
Mouse motion None
Left click Zoom: zooms in at the selected point

Tool: Jumps the slice window to the selected slice

Left click and drag Zoom: zooms to the selected region

Tool: Jumps the slice window to the selected slice

Right click Zoom: zooms out at the selected point

Tool: Jumps the slice window to the selected slice

Right click and drag Zoom: zooms out at the selected point

Tool: Jumps the slice window to the selected slice

'ctrl-z' Zooms to full dataset (similar to a "home" function).
'z' Enter zoom mode

TRW-S

The options for this tool are:

Option Description
Max Loops The number of loops that the TRW-S algorithm will run. One loop corresponds to just one pass through the data; for example, the left-and-then-down pass.
Slice range A range of slices relative to the current slice that the tracker will be applied to. This field is ignored when the surface view is used to apply TRW-S since the selected region will determine the slice range in this case.
Normalization Normalization range...
GT Range Ground truth (GT) range that the surface may pass through. +/- this many bins will be allowed.
CT Smooth Cross-track (CT) smoothing weight
AT Smooth Along-track (AT) smoothing weight
Tomo Layers Layer structure (see opsLoadLayers) to load two layers for constraining the search.
Select If true, only the selected elevation angle bins will be effected by the tracking. If false, all elevation angle bins will be updated regardless of the selection.
L,R,T,B Applies boundary conditions for left (L), right (R), top (T), and bottom (B) respectively that ensure that the new tracking result merges into the existing two way travel times on the corresponding boundary.

Basic Radar Interpretation

The root of picking is interpretation of radar data. This can be very tricky and can only be developed with practice. Below we will give some basic examples of common interpretation situations and how they should be picked. After reading through this section you should be ready to do the Interactive Picking Tutorial with the help of someone who has picked a lot and can guide you. How to use this tutorial will be explained later.

Procedure:

  1. Pick the surface over smooth ice using CSARP_standard and snake. The reason to use CSARP_standard over smooth surfaces is because CSARP_mvdr tends to self-null and distort bright reflections. If the terrain is mountainous, the surface should be picked with CSARP_mvdr and snake. Use the "Image Params" feature to smooth the image with the along-track averaging set to 4. Set the "snake range" in the Tool Params to 1 or 2. Where snake fails, use interp.
  2. Pick the bottom using CSARP_mvdr and snake. Use minimal "Image Params" smoothing (along-track averaging set to 2 and range-bin averaging set to 1). Set the "snake range" in the Tool Params from 5 to 25 depending on the steepness of the topography (larger for steeper). Where snake fails, use interp. When the bottom merges with the surface, use the convert tool to make the bottom exactly equal to the surface. The "(a)ll" hotkey is useful for dealing with transitions between merged and unmerged ice surface/bottom layers.
  3. Set the quality level of the data. If the location of the layer is unambiguous, the quality is "good/green". If there is a wide spread in the layers return (hundreds of meters), then the quality is "moderate/yellow". If the layer scattering is not clear and you are relying on other sources of information (e.g. neighboring picks and u-shaped channel assumption, seismic data, mass conservation, etc.) to track the layer, the quality is "derived/red".
  4. Quality control

Examples

Simple Ice Surface and Bed

Simple ice surface should be automatically picked by the radar processing. If it is not you will have to pick it. Usually for very clear surfaces the best method is to use max point to enter a few points along the layer and then snake to interpolate across the entire layer. The example below was done with this method.

Simple surface echo picks.pngSimple surface echo.png

Ice/Rock Interface

Often in the data the flightpath transitions from being over ice to over rock or water. When this happens the surface and bottom layers become the same. We use a separate layer type "both" or "a" to represent both surface and bottom exactly the same. This can be tricky when picking very rocky areas, but a simple transition is shown below. You can see there is separate bed and surface on the left and then a single combined layer on the right over rock. It is important to note that this interface does not always match up with the GeoTIFF because the GeoTIFF's are old and out of date.

Simple icerock echo.pngSimple icerock echo picks.pngSimple icerock map.png

Surface and/or Bed Multiples

Multiples refer to signals that resonate or reflect between two surfaces. Most commonly this is between the air plane wing and the ice surface. Both are large and flat and so create a strong reflection. For ice surface and bottom tracking, the signal we desire is the signal that travels from the radar to the target and then back to the radar and is received. However, a portion of the return signal will reflect on the large metal aircraft and travel back to the scene and reflect off the scene AGAIN and travel back to the radar and be recorded. For very flat surface and/or high dielectric contrast surfaces, the signal may reflect back and forth between the radar platform and the scene several times. Multiples also include reflections between the ice surface and ice bottom. This is most common on ice shelves where the ice is thin and flat and reflected signal is coherent and therefore strong in the vertical direction. For the typical situation we will have three returns:

  1. Surface return at T_surface two way travel time delay. For 500 m altitude above ground level (AGL), this is about 3e-6 seconds.
  2. Bottom return at T_bottom > T_surface delay since the ice bottom is below the ice surface and therefore is further away.
  3. Surface multiple at 2*T_surface delay. The signal travels to the surface, back to the plane, reflects off the plane and travels back to the surface, and then back to the plane.

Therefore to distinguish between the ice bottom and the ice surface, one should look for a signal that looks like the surface, but is twice the delay.

For thin ice shelves the situation can get much more complicated, but by carefully considering all possible bounces that can occur between plane, surface, and bottom, the causes for each signal return can usually be determined. This becomes tricky when the signals overlap and it is hard to tell which one may be causing a reflection. In some situations it is still clear because the ice bottom may look very different in nature. However, in other situations you may need to lower the quality level of the tracked layer or even not track the layer at all if it is completely ambiguous.

Simple surfmult echo.pngSimple surfmult echo pick.png

Gaps In Bed

Often in hard to sense regions there will be gaps in the layers that we cannot pick with enough confidence to include in our data product. The example below shows a frame where there is a small gap in the bed that should not be picked. This frame also shows a good example of multiple surface multiples, including one that is at the same level as the real bed layer.

Simple bedgap echo.pngSimple bedgap echo pick.png

Difficult to Pick Bed

Often the bed is difficult to pick. It may contain lots of gaps, scattering, and other features that make determining a single valid layer difficult. There are a few tricks when trying to pick difficult bed layers.

  1. Follow the layer. You should pick the layer you think is most likely the bed and follow that layer through the frame.
  2. Don't overpick. Leave gaps where there are gaps. (Note these) They may be filled in later by someone with more experience.
  3. Zoom in to a good level (IMPORTANT!) to pick the bed, however don't forget to zoom in and out to keep track of the layer you're picking.
  4. Use all the processing tools available. (MVDR,DETRENDING,etc...)

The example below is just one of many examples of difficult bed picking.

Simple difficultbed echo.pngSimple difficultbed echo pick.png

Scattering

Scattering often creates a difficult to pick bed and/or surface. The images above and below both contain scattering that makes picking difficult. The image below shows englacial liquid water scattering. It can often be identified by its non-topographic appearance and very diffuse/pattern-less scattering. The liquid water also attenuates the signal through both dielectric loss and signal extinction from scattering away the energy. The best way to identify this scattering is to look for a bed signal underneath it where the signal is still large enough to still detect a bed as in the example below.

Simple scattering echo.pngSimple scattering echo pick.png

Picking Tutorial

TYPE FRAME Information about FRAME Solutions
T 20110326_12_005 Introductory Bed Picking. 20110326_12_005
T 20110329_01_014 Introductory Ice/Rock Interface. 20110329_01_014
T 20110329_02_017 Moderate Bed Picking. 20110329_02_017
T 20110331_02_011 Non-Continuous Bed Picking. 20110331_02_011
20110331_02_012 Non-Continuous Bed w/ scattering. 20110331_02_012
20110331_02_016 Non-Continuous Bed in a channel. 20110331_02_016
20110331_02_019 Non-Continuous Bed and surface multiple interference. 20110331_02_019
20110331_02_031 Difficuly Bed Picking. 20110331_02_031
20110422_02_021 Difficult Bed Picking. 20110422_02_021
20110426_11_006 Moderate Bed Picking. 20110426_11_006
20110502_01_019 Introductory Bed Picking. 20110502_01_019
20110502_01_022 Difficuly Bed Picking. Lots of Scattering. 20110502_01_022
20110507_02_014 Floating Ice and Bed Multiples. 20110507_02_014
T 20110509_01_019 Icebergs. Should we pick them? No, but Why? 20110509_01_019
T 20110509_01_020 Floating v. Grounded Ice, Bed Multiples. 20110509_01_020
20110509_02_009 Ice Caps, Strong Surface Multiple. 20110509_02_009
20110509_02_010 Surface Multiple. 20110509_02_010
T 20110510_02_018 Ice Caps. 20110510_02_018
20110510_03_002 Moderate Bed Picking. Ice/Rock Interface. 20110510_03_002
20110510_03_007 Surface Multiple Interaction with Bed. 20110510_03_007


Layers

standard:surface: The earth surface (also the ice surface).
standard:bottom: The bottom of the ice. Where there is no ice, standard:bottom equals standard:surface. Ice bergs are not currently tracked reliably.
standard:bottom_qc: Used for QC process with ice bottom.
standard:GIMP: Surface layer from the Greenland Imaging Project
standard:Bedmap2: Surface layer from the Antarctica Bedmap-2 project.
standard:gravity: Bottom estimated from gravity inverse modelling.
standard:mc_bottom: Bottom estimated from mass conservation.
iceberg:iceberg: Ice bergs
lidar:atm: LIDAR surface (often from Airborne Topographic Mapper)
automatic:*: Used for automatic tracking.

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