NEXRAD and TRMM Rainfall Process
Use the NEXRAD data, ground based 1-4sqkm resolution, hourly to 5 minutely
The Java NEXRAD Viewer allows viewing binary files and exporting as ASCII GRID or Shapefile for manipulation
·
NEXRAD Viewer
Process is the location to launch your work – get the viewer, links to
data, etc.
o
Retrieve Data Map chose
the appropriate site for your analysis, then find active rainfall periods to
download
o
Perform analysis and exports
Use the TRMM 3B42 data product, spaceborne coverage at 0.25 degree spatial resolution, 3 hour temporal
·
TRMM
data for online visualization and analysis
o
Fill in your N, W, S, E coordinates, select Accumulated Rainfall, Plot
as a time-series, and generate ASCII output.
Archived Details – some may be expired links
Products Derived from National Weather Service NERFC
· Hydrometeorological Discussion
o Stage 3 Recent Product Imagery
o The
stage I, stage III and MPE data files are collected from the RFCs. The files collected contain a day's worth of data
which is made up of UNIX compressed hourly files that are tarred into a single
file. The daily files are then tarred together to create a monthly file which
is available on the web. The table below shows the date range of the archived
data.
o Quick descriptions of the data files for stage I data and stage III data are available. For more detail information concerning data formats and decoding procedures, see Precipitation Processing System, NEXRAD Stage III Precipitation Data and HRL Distributed Modeling Research online documentation. (Note: Please view the National Weather Service Disclaimer regarding the information on this US Government Server.)
§
DS.81dpr/ is the product of 1 hourly digital rainfall. The U.S. National Weather
Service provides anonymous FTP access to files containing collectives of code
generated and binary radar imagery products from NWS, FAA, and DOD WSR-88D
sites located in the
§
Decoders are
available for WSR-88D products
§
Data
available from HDSS Access System
o
Quantitative Precipitation Products
·
GIF imagery of all storm events to determine whether retrieval of Stage
III data.
§
Perform analysis and exports
o Stage
I Data
Stage I data comes in two types: encoded and decoded. The encoded products are
the hourly digital precipitation (HDP) products which are transmitted to the
RFC via AFOS. After the receipt of the encoded products, the RFC decodes and
stores the information. The decoded products contain only a subset of the
encoded products and so NHDS stopped archiving the decoded products as of
February 1996. Only the encoded products are available on the web.
o Stage III Data
§ HRL Distributed Modeling Research
§ Distributed Model Intercomparison Project
o Multisensor Precipitation Estimator Data
Displaying and Using NWS
XMRG/HRAP Files
within ArcView or Arc/Info GIS
Created: 11/26/1999
Last Modified: 1/28/2002
ESRI Software Built-in
Projection Capabilities (Differences between Arc/Info and ArcView)
Approaches for
displaying XMRG/HRAP data in ArcView
Scenario
1. I have Arc/Info software as well as ArcView
3.1 with the Spatial Analyst. I want to display XMRG/HRAP precip
files as Grids in ArcView and overlay vector
data. I have access to Arc/Info software as well as ArcView
3.1 with the Spatial Analyst.
-
C Programs for XMRG to Grid conversion
-
An Arc/Info Projection file for HRAP
Scenario 2. I want to display XMRG/HRAP precip files as Grids in ArcView
and overlay vector data. I only have ArcView
3.1 software with the Spatial Analyst extension (No Arc/Info).
- An ArcView Extension for working with HRAP Coordinates
Scenario 3. I want to determine which HRAP cells
fall within my basin or display HRAP-based data in another coordinate system (I
do not have Arc/Info).
BACKGROUND
Several people have
asked: How can I display and use XMRG files in ArcView?
This web page is intended to answer questions about XMRG, HRAP, and ArcView. XMRG is a binary file
format used within the National Weather Service to store gridded data.
More specifically, gridded rainfall products like NEXRAD StageIII
are sometimes stored in the XMRG format. HRAP (Hydrologic Rainfall
Analysis Project) is a grid coordinate system used within the National Weather
Service. One way that the HRAP grid is used is to define the location of StageIII rainfall cells. IMPORTANT POINT: XMRG
is a file format and HRAP is a coordinate system. Gridded data that is
not referenced to the HRAP coordinate system could be stored in XMRG
format. Gridded data referenced to the HRAP coordinate system may be
stored in other file formats (e.g. netCDF and
GIF). This page describes several programs that make it easier to work
with data referenced to the HRAP grid and stored in XMRG format. Several
of these programs are also useful if you have data referenced to HRAP in a
non-XMRG format.
The paper: Reed, S.M.,
and D.R. Maidment, "Coordinate Transformations for Using NEXRAD Data in GIS-based
Hydrologic Modeling," Journal of Hydrologic Engineering, 4, 2,
174-182, April 1999, offers details about how the HRAP coordinate is defined
and insights as to why displaying HRAP grids with GIS data has been a
point of confusion. It is not necessary to read and fully understand this
paper to correctly apply the programs provided this page (although it is
helpful to have a basic knowledge of map projections and how they are
implemented using ArcView and Arc/Info). For those of
you who have looked at this paper, there are a few misleading statements that
could not be corrected before publication. The discussion revolving
around Figure 6 in this paper incorrectly implies that radar data are mapped by
drawing a circle representing the radar range in the HRAP plane. In the
actual NWS radar software, the longitude, latitude coordinates corresponding to
radar estimates are computed on a radar-centric polar grid using equations for
a spherical earth prior to projecting data into the HRAP coordinate system.
The HRAP grid is used primarily for mosaicing and
displaying rainfall values. As long as distances are not measured in the
HRAP plane, the "scale factor" problem described in relation to
Figure 6 is not an issue. With this out of the way, the main point of
this page is to provide tools to work with data sets referenced to the HRAP
grid using the standard GIS software packages ArcView
and Arc/Info.
ESRI Software Built-in
Projection Capabilities (Differences between Arc/Info and ArcView)
The methods and
programs described on this page were devised keeping in mind the capabilities
inherent to ESRI software (Arc/Info and ArcView),
taking advantage of these capabilities where possible. Arc/Info 7.0 or
higher provides excellent support for map projections
and coordinate transformations. ArcView 3.1 is
more limited in that it only allows projection of vector data (not raster data
i.e., Arc/Info Grids) and has more limited built-in flexibility in defining
input and output projection parameters. Even projecting vector data
Themes in ArcView 3.1 is not part of the base
software functionality (Note that when I say projecting data Themes I mean
actually creating a new data set, not redefining how Themes are displayed in a
View); however, some Theme projections can be done using the free
"Projector!" extension distributed by
ESRI or using Avenue. ArcView 3.2 is supposed
to have improved support for map projections, but it is unclear whether the
ability to project Grids will be included in future versions of the Spatial
Analyst.
Approaches for
displaying XMRG/HRAP data in ArcView
The common problem
that is being addressed here is that that precipitation grids
are often available in XMRG format and referenced to the HRAP grid, and it is
often desirable to display and/or analyze these precipitation grids along with
other data sets (e.g. state boundaries, watersheds, streams, gage locations)
that are not commonly available in the HRAP coordinate system. To provide
a consistent framework for analysis, either the rainfall grids or the
"other" data must be re-projected. It may or may not be
desirable to keep the precipitation data in a gridded file format.
Here are some
scenarios that the programs described below will support. Certainly,
other scenarios may be more appropriate depending on the intended application
and available software.
Scenario
1. I have Arc/Info software as well as ArcView 3.1 with the Spatial Analyst. I want to display
XMRG/HRAP files as Grids in ArcView
and overlay vector data. I have access to Arc/Info software as well as ArcView 3.1 with the Spatial Analyst.
Scenario
2. I want to display XMRG/HRAP precip files as Grids in ArcView
and overlay vector data. I only have ArcView
3.1 software with the Spatial Analyst extension (No Arc/Info).
Scenario
3. I want to determine which HRAP cells fall
within my basin.
Scenario
1. I have Arc/Info
software as well as ArcView 3.1 with the Spatial
Analyst. I want to display XMRG/HRAP precip files as
Grids in ArcView and overlay vector data. I
have access to Arc/Info software as well as ArcView
3.1 with the Spatial Analyst.
The first step in both
Scenarios 1 and 2 is to convert an XMRG file (in the HRAP coordinate system) to
Arc/Info Grid format. A C program called xmrgtoasc.c
can be used to translate XMRG files to an ASCII file format that can be
imported into ArcView. xmrgtoasc.c creates a file with the ".asc" ending. The program takes three arguments:
input file name, output file name, and the key word "ster"
or "hrap."
Example syntax used to
compile on HP Workstations: cc -Aa
-o xmrgtoasc xmrgtoasc.c
Example execution syntax: xmrgtoasc <infilename> <outfilename>
ster
The resulting files
can be loaded into ArcView by clicking the File-->
Import Data Source menu item when the Spatial Analyst is loaded and a View
is active. Select "ASCII Raster" as the import file type.
The HRAP grid is
defined in the plane of a polar stereographic map projection with the following
parameters:
longitude of the projection center = -105, standard (true) latitude = 60
N. A spherical earth of radius 6371.2 km is assumed in defining the HRAP
coordinate system. Using "ster" as
the third argument to the xmrgtoasc.c program
generates header information in Polar Stereographic coordinates with units of
meters. The "hrap" argument generates
header information in HRAP units. These Polar Stereographic coordinates
are related to HRAP coordinates as follows:
xster=hrapx*4762.5 - 401*4762.5
yster=hrapy*4762.5-1601*4762.5
Having grids available
in Polar Stereographic coordinates makes it possible to use the Arc/Info
Project function to project gridded data; however, this requires tricking
Arc/Info. (Thanks to Tom Evans at HEC for suggesting this
approach.) The HRAP projection is defined using a sphere of radius
6371200 m and using a true latitude of 60 N.
Arc/Info does not support customizing both the sphere radius and the true
latitude when using the Polar Stereographic projection. The default
radius for a sphere used by Arc/Info is 6370997 m. The "trick"
is to use the Arc/Info default radius and a true
latitude that is slightly different than 60 N as shown in the projection file
below to approximate the HRAP definition. This projection file closely
approximates the conversion from the HRAP defined Polar Stereographic
coordinates to geographic coordinates. This is particularly useful when
dealing with grids because it allows a user to take advantage of the resampling capabilites of
Arc/Info when projecting grids. Differences between using this
"trick" projection file and the exact equations are negligible at 33
N (~0.4 m differences were found when comparing these results to the exact
transformation for single points). It appears that this trick cannot be
used within Avenue to project Shapefiles because ArcView doesn't support a polar Stereographic projection
where you can specify the true latitude. Programs for transforming Vector
data using Avenue are described below in Scenario 2.
/* Example projection file
input
projection polar
spheroid sphere
units meters
parameters
-105 0 0
/* longitude of the center of the projection
60 0
24.5304792 /*
true latitude dd mm ss
0.0
/*false easting
0.0
/*false northing
output
projection geographic
spheroid sphere
units dd
parameters
end
Scenario 2. I want to display XMRG/HRAP precip files as Grids in ArcView
and overlay vector data. I only have ArcView
3.1 software with the Spatial Analyst extension (No Arc/Info).
Under certain
circumstances, it may be desirable to leave the gridded data in HRAP or Polar
Stereographic coordinates and convert reference vector data sets to this
coordinate system. To implement this scenario:
- Use one of the C
programs described in Scenario 1 (xmrgtobin.c or xmrtogasc.c) to create Arc/Info Grids from XMRG files in
HRAP coordinates
Note: ArcView supports a Polar Stereographic projection but not
the type used by HRAP which requires specification of a
"true" latitude.
- Project Point,
Line, or Polygon shapefiles from geographic
coordinates to HRAP coordinates using scripts provided in the
coord.avx extenstion.
(Place this file in the ArcView/ext directory (PC or
UNIX) or your home directory(UNIX)). If you load
the extension coord.avx (Listed as "Sp-coord" in the Load Extensions dialog) you will see one
new Menu called "HRAP" with one Item -- "Create HRAP
Center Points," two new Buttons "G/H" and
"G/A," and a new Tool Menu with the Tools "H/G"
and "G/H." The G/H button
will project active Point, Line or Polygon Shapefile Themes into the HRAP coordinate
system. Note, this program may take a while for
large data sets because it cannot take advantage of pre-compiled Avenue
requests.
Note: The H/G and G/H Tools can be used to
click a point on the map and return the geographic coordinates of the point
clicked if the display is in HRAP ( H/G ) and return the HRAP coordinates of
the point clicked if the display is in geogaphic (
G/H ). Other features of this Extension are described in Scenario 3.
Scenario
3. I want to determine
which HRAP cells fall within my basin or display HRAP-based data in another
coordinate system (I do not have Arc/Info).
Scenario 3 stems from
my work on Threshold
Runoff (threshR) where it is desirable to do the
basin delineation and spatial analysis in an Albers Equal-Area
projection. For threshR, it is necessary to
know the location of the center points of HRAP cells in the Albers Equal-Area
projection. To do this, a Shapefile of HRAP center points is created and
projected from HRAP to geographic (lon-lat) and from
geographic to Albers.
1. Using the coord.avx extension described in Scenario 2, select the
Menu item HRAP --> Create HRAP Center
Points. This program gives the option to create a Shapefile of HRAP
center points in HRAP coordinates, polar Stereographic coordinates, or
geographic coordinates (lon-lat). The extent of
the Shapefile to be created can be specified by (1) longitude and latitude
extent or (2) the lower left HRAP coordinates and the number of columns and
rows (The second approach is preferred because of issues explained in step 3
below).
2. (Skip this step if
you want to work in geographic coordinates.) Create a (lon-lat) center point shapefile in Step 1 and project this
into an Albers Equal-Area projection using the Button G/A. Note that
specific Albers parameters are hard coded into this program. For ThreshR, the locations of the HRAP center points are needed
so that threshold runoff values can be interpolated to these points. The
center point coverage can also be used to automatically identify the HRAP cells
falling within a basin. It is also possible to join XMRG data values to
the center-point Shapefile to graphically display storms as described in Step
3.
3. To join XMRG
data values to an HRAP shapefile, a comma delimited text file with at least two
columns must be created. One column contains a unique ID to join to the
HRAP shapefile and the other a set of XMRG data values. A C-program
called xmrgtolist.c will create a comma delimited text
file from an XMRG file. The compile syntax is in the file header and the
run syntax is: xmrgtolist <infile>
<outfile>. (Note: you should give the "outfile" a ".txt" extension). The xmrgtolist program creates unique IDs for all hrap cells by numbering from the lower left corner, across
columns, up one row, etc. The ArcView menu item
Create HRAP Center Points (Step 1) uses the same numbering scheme;
however, to be able to join the values in the ".txt" file to the
center-points Shapefile, the center-points shapefile must be created with the
exact same extent (number of columns and rows) as defined in the XMRG file,
otherwise the join ID's may be inconsistent. Load
the output from xmrgtolist into ArcView
by clicking on Tables and then Add in the
Project window. Join the resulting Table to the center-point Shapefile
using Table-->Join. The XMRG data can now be displayed by manipulating
the legend of the center-point Shapefile. The Shapefile could be
converted to a grid at this point (faster display), but you can get a pretty
good visually display using the point data alone.
ESF Work on Scan
