MERLIN: A Display System for Environmental Data

David Santek, Kenneth Bywaters, Susan Gorski, Kristine Gould,
Matthew Lazzara, Beth O'Brien, J.T. Young

Space Science & Engineering Center
University of Wisconsin
Madison, Wisconsin


As we enter the EOS (Earth Observing System) era, data handling and scientific tools are concerns at the forefront. We at the SSEC (Space Science and Engineering Center) have long held the philosophy of interuse. Which isthe ability to use data from various sensors and scientific disciplines for research. Interuse is made possible by providing tools to the scientist to allow intercomparsion, visualization and data fusion of disparate data. This may mean collecting remotely sensed data along with observations or model data, and presenting it for analysis or generating a product. Transforming coordinates or deriving new quantities from the original data may be required for effective interpretation. This need resulted in the development of MERLIN, (Multi-source EnviRonmental data DispLay for INternet archives). MERLIN empowers the researcher with a means to not only visualize data, but also to process, correlate and analyze. During the design and implementation of this software package, special emphasis was given to its use with the NASA/NOAA Pathfinder data set. MERLIN is freely available in a binary format for a variety of Unix platforms. The interface is an intuitive graphical user interface.


When MERLIN is started, the user is presented with two windows: a Control Window and an Image Window. The Control Window is used to initiate requests to display or compare data, and derive products. The Image Window provides pictorial representations of remotely sensed data with graphic overlays of ancillary data. Most actions are performed through point-and-click, usually by selecting from lists. This reduces the chance of user error by presenting only valid choices. All actions to the Image Window or the data will be accomplished through an application interface dialog box. Each item of the user interface has online documentation to aid the user in understanding the interface

2.1 Image Window

The initial size of the MERLIN Image window is 640x480 pixels. Four 640x480 frames are stored in memory; each frame can be loaded with a different image and overlay. Only one frame can be displayed in the window at one time. Frames can be stepped through individually or looped at a fast rate. The image can be disabled to see the graphics on a black background, and the graphics can be disabled to see the image without any overlayed graphics. More frames of any size may be created with the configuration option on the Window Menu.

2.2 Control Window

The Control Window is the graphical interface to the MERLIN software. It is composed of three parts: the Control Panel, the Data Menu, and the Window Menu. The Control Panel contains buttons to quickly control frame looping, select a frame to view, erase graphic overlays or toggle between image and graphics displays. The interface contains VCR style buttons to loop forwards or backwards, and advance or back up one frame at a time. There is also a Help button that describes the functions of the Control Panel and the applications available through the menus.

2.2.1 Data Menu

The Data Menu is used for displaying modifying and listing data.

Displays may be comprised of the following data:

* images

* grids

* point source data

* GIF files

* meteorograms

* skew T diagrams

* cross sections

The following modifications can be made to the data:

* perform arithmetic operations on a grid

* change a grid to an image

* combine or subsect images

* generate image products

* remap or rotate an image

The following data can be listed:

* surface

* upper air

The Data menu contains a button for each action. When a raised button specifying an action is clicked, the valid data types for this action are presented in a menu. Clicking on a data type within an action will bring up the corresponding application dialog box.

2.3.2 Window Menu

The raised buttons in the Window Menu contain all the functions that can be performed on the Image Window. The Colors option allows the user to alter the color enhancement, or graphics colors on a frame. The Graphics option can be used to erase graphics from the frame, draw a map over an image, or do freehand drawing on a frame. Geolocation and physical quantities associated with the pixels on the image can be viewed by using the options in the Inspect Data menu. Options available under Configuration include: loop sequence configuration, X font configuration, cursor and graphics parameter settings, and list workstation configuration.

2.3 Application Interfaces

Each menu item from the Data Menu or Window Menu will bring up a dialog box for the action. The dialog boxes consist of entry fields, buttons, and sliders. Entry fields are either required or optional, and are distinguished by shading. The required fields must be filled in for the application to run; the user is notified if any are left blank. Most entry fields are not entered manually; they can be selected from a menu. Clicking a raised buttons will access the menu or dialog box associated with it. The Show Image window in the diagram illustrates a typical command interface dialog box. When the Image button is pressed, a File Listing window is presented. A file can then be selected by double clicking on a file name. If the image in the file is mult-banded, another File Listing window is displayed containing the bands listed in the file. The Show Image window also contains a slider to allow the user to scale the displayed image.

2.6 Online Documentation

Each Menu has a corresponding help window that explains each menu item. A general overview of MERLIN can be obtained from a button press. Each command dialog box has an associated help button which when pressed, brings up a window explaining all fields and buttons in the dialog box.


MERLIN operates on several different data formats.

Imagery in the following formats can be displayed:

* Pathfinder data in HDF (Hierarchical Data Format)

AVHRR (Advanced Very High Resolution Radiometer)

SSM/I (Special Sensor Microwave Imager) antenna temperatures

SSM/I rain rates

SSM/I sea ice concentrations

HIRS/2 (High Resolution Infrared Radiation Sounder)

MSU (Microwave Sounding Unit)

* McIDAS (Man computer Interactive Data Access System) image files

* GIF (Graphic Interchange Format) files

* McIDAS point source data

* McIDAS grids


MERLIN is currently supported on the following configurations:

Workstation Operating System

Sun SPARCstation SUNOS version 4.1.3, Solaris 2.3

IBM RISC System/6000 AIX version 3.2.3

SGI IRIX version 4.0.5 and 5.2

HP/Apollo 9000 Series 700 HP-UX version 9.01 and 9.03

The user interface to MERLIN was created using the Tcl/Tk package developed by John Ousterhout of the University of California - Berkeley (Ousterhout, 1994). Motif applications are used for information and error messages generated by MERLIN processes.


MERLIN is distributed freely (binary only) via anonymous ftp:


login: anonymous

password: myname@mylocation

ftp> cd pub/Merlin1.0

ftp> get README

ftp> get merlin1.0.readme

ftp> bye

The README file contains information on the MERLIN ftp directory structure.

The merlin1.0.readme file contains instructions for obtaining and installing MERLIN.

Questions and comments can be directed to


MERLIN was developed as a scientific tool for researchers investigating global change and climate issues. MERLIN development continues with more data types planned for the future. Additional functions and enhancements to existing functions are being investigated. Early reviews of MERLIN by researchers are favorable. MERLIN is the core for additional interfaces targeted at other research groups. These include interface sidecars for MODIS (Moderate Resolution Imaging Spectroradiometer) and AMRC (Antarctica Meteorological Research Center) (Bywaters, et al., 1995) research.


MERLIN was developed by the University of Wisconsin - Madison Space Science and Engineering Center (SSEC) with principle funding from the National Aeronautics and Space Administration (NASA), National Oceanographic and Atmospheric Administration (NOAA) and the National Science Foundation (NSF).


Ousterhout, J.K., 1994: Tcl and the Tk Toolkit, Addison-Wesley, 458 pp.

Bywaters, K. W., M. Lazzara, D. Santek, J. T. Young, 1995 An Antarctic Data Archive and Access System. Preprints, Eleventh International Conference on Interactive Information and Processing Systems for Meteorology, Oceanography and Hydrology, Dallas, TX.

Preprints, Eleventh International Conference on Interactive Information and Processing Systems for Meteorology, Oceanography and Hydrology, Dallas, TX.