USGS Mercury Relief

Usage

You access the global Messenger relief grid by specifying the special name

@mercury_relief[_rru[_reg]]

This grid contains observed relief measured via altimetry. The following codes for the optional rru and reg are supported (dimensions are listed for pixel-registered grids; gridline-registered grids increment dimensions by one):

Code	Dimensions	Reg	Size	Description
01d	360 x 180	g,p	114 KB	1 arc degree Mercury relief (Messenger @ 315 km)
30m	720 x 360	g,p	401 KB	30 arc minute Mercury relief (Messenger @ 157 km)
20m	1080 x 540	g,p	839 KB	20 arc minute Mercury relief (Messenger @ 105 km)
15m	1440 x 720	g,p	1.4 MB	15 arc minute Mercury relief (Messenger @ 79 km)
10m	2160 x 1080	g,p	3.0 MB	10 arc minute Mercury relief (Messenger @ 52 km)
06m	3600 x 1800	g,p	7.9 MB	6 arc minute Mercury relief (Messenger @ 32 km)
05m	4320 x 2160	g,p	11 MB	5 arc minute Mercury relief (Messenger @ 26 km)
04m	5400 x 2700	g,p	17 MB	4 arc minute Mercury relief (Messenger @ 21 km)
03m	7200 x 3600	g,p	29 MB	3 arc minute Mercury relief (Messenger @ 16 km)
02m	10800 x 5400	g,p	63 MB	2 arc minute Mercury relief (Messenger @ 11 km)
01m	21600 x 10800	g,p	224 MB	1 arc minute Mercury relief (Messenger @ 1.9 km)
56s	23040 x 11520	p	262 MB	56.25 arc second Mercury relief (Messenger @ 1.9 km)

Note that resolutions 05m and higher are tiled. See Remote Datasets for more information.

See GMT remote dataset usage for when resolution codes are optional or required. All of these data will, when downloaded, be placed in your ~/.gmt/server directory, with the mercury_relief files being placed in an mercury/mercury_relief sub-directory. If you do not specify a CPT then the default CPT for this dataset (the GMT master @mercury_relief.cpt CPT) will be used.

Examples

To create a PDF map of the Mercury Messenger relief at 1 arc degree resolution, try:

gmt grdimage @mercury_relief_01d -Baf -pdf mercury_relief

Technical Information

As you see, the 01m and lower resolutions are all derivatives of USGS’ 56.25 arc-second Mercury_Messenger_USGS_DEM_Global_665m_v2.tif (Becker_et_al.,_2016). We have downsampled it via Cartesian Gaussian filtering to prevent aliasing while preserving the latitude-dependent resolution in the original 56.25 arc sec grid. The full (6 sigma) filter-widths are indicated in parenthesis. Almost all grids are available in both gridline- and pixel-registered formats except the original pixel-registered grid at 56.25 arc-seconds resolution (here called @mercury_relief_56s).

We also scale and reformat the original data to take up very little space so that downloads from the servers are as fast as possible. For the mercury_relief grids this means we chose 0.5 meter as the grid z step, which is well below the uncertainties in the data. Elevations are scaled and shifted to fit in a short integer grid that is highly compressed by netCDF lossless compression and chunking.

Note: Because of this quantization, these grids should be used with care in morphometric studies (e.g., slope, curvature or roughness analyses), since even sub-meter rounding can bias slope and aspect calculations [Carter, 1992]. We suggest using the original dataset instead for such applications.

Data References

1. Carter, J.R., 1992: [https://doi.org/10.3138/aj35-34h3-524k-0685].

2. Messenger: [https://www.hou.usra.edu/meetings/lpsc2016/pdf/2959.pdf].