LRO LOLA Gridded Data Record Shape Map (GDRDEM)

GDRDEM – Gridded Data Record Shape Map

Instrument: Lunar Orbiter Laser Altimeter

PDS Data Set ID: LRO-L-LOLA-4-GDR-V1.0

For more information about LOLA RDR and derived products, see the RDR Product SIS.

For more information about all LOLA products, see the LOLA Archive Volume SIS.

The Lunar Orbiter Laser Altimeter (LOLA) Gridded Data Records (GDRDEM) data products are map-projected digital elevation models (shape models) derived from altimetry data acquired by the LOLA instrument. Each product uses data acquired through various mission phases. The GDRDEM data products contain the binned, interpolated altimetric measurements on a uniformly-spaced grid.

A pixel in the GDRDEM product represents the mean value at the center of a region bounded by lines of constant longitude and latitude at integral numbers of degrees or fractions thereof, scaled and interpolated where necessary. The size of the products at higher resolutions requires that they be aggregated in subsets of global coverage. Global standard products use the Equirectangular map projection, also known as Simple Cylindrical, while the higher-resolution products afforded by dense polar coverage use the Polar Stereographic projection.

The resolution of equirectangular pixels is in powers of two pixels per degree of longitude and latitude (e.g. 4, 16, 64, 128, 256, 512, and 1024). The resolution of polar projected pixels is in integral numbers of meters at a radius of 1,737,400 m, true at the pole. The pole is a point surrounded by the four central pixels, and the colatitude of a pixel at a distance r meters from the north pole is simply 2arctan(0.5r/1,737,400). Polar stereographic projections are produced at latitudes from 45 degrees to the poles.

Equirectangular map-projected digital elevation models

Product

Pixel size (latitude)

Number/size of tiles

Bits per pixel

LDEM_4

7.5808 km

Global, 0-360

16

LDEM_16

1.895 km

Global, 0-360

16

LDEM_64

0.4738 km

Global, 0-360

16

LDEM_128

0.2369 km

Global, 0-360

16

LDEM_256

118.45 m

4 tiles, longitudes 0:180:360 by N/S

16

LDEM_512

59.225 m

Longitudes 0:90:180:270:360 by 45° latitude bands

16

LDEM_1024

29.612 m

Longitudes 0:30:60:90:120:150:180:210:240:270:300:330:360 by 15° latitude bands

16

Selection of polar map-projected digital elevation models, N/S

Product

Dimensions

Pixel size

Latitude range

Bits per pixel

LDEM_45S_100M

28880 x 28800

100 x 100 m

+/- 45° to pole

16

LDEM_60S_60M

31040 x 31040

60 x 60 m

+/- 60° to pole

16

LDEM_75S_30M

30496 x 30496

30 x 30 m

+/- 75° to pole

16

LDEM_80S_20M

30400 x 30400

20 x 20 m

+/- 80° to pole

16

LDEM_85S_10M

30336 x 30336

10 x 10 m

+/- 85° to pole

16

LDEM_87S_5M

30336 x 30336

5 x 5 m

+/- 87.5° to pole

16

Additionally, there is one product which is projected into the dynamically defined Principal Axis coordinate system for consistency with all lunar gravity spherical harmonic models. The product is named LDEM_64_PA.IMG, with its corresponding label file.

LOLA GDRDEM global products have the following file names:

productsuffix

where:

product = product name above

suffix = file type/extension

_FLOAT.IMG = floating point image file

_FLOAT.LBL = detached PDS label

.IMG = image file

.LBL = detached PDS label

.JP2 = JPEG2000 file

_JP2.LBL = detached PDS label

LOLA GDRDEM regional products have the following file names:

product_mmmd_nnnd_www_eeesuffix

where:

product = product name above

mmm = minimum tile latitude in degrees

d = direction of minimum latitude

N = north

S = south

nnn = maximum tile latitude in degrees

d = direction of maximum latitude

N = north

S = south

www = westernmost longitude in degrees

eee = easternmost longitude in degrees

suffix = file type/extension

_FLOAT.IMG = floating point image file

_FLOAT.LBL = detached PDS label

.IMG = image file

.LBL = detached PDS label

.JP2 = JPEG2000 file

_JP2.LBL = detached PDS label

In ODE, GDRDEM products have one of the following product IDs:

PRODUCT (images and JPEG2000s)

PRODUCT_MMMD_NNND_WWW_EEE (regional images and JPEG2000s)

PRODUCT_FLOAT (floating point images)

PRODUCT_MMMD_NNND_WWW_EEE_FLOAT (regional floating point images)

Note: Conversion from Digital Number to HEIGHT i.e. elevation in meters, is:

HEIGHT = (DN * SCALING_FACTOR).

The conversion from Digital Number to PLANETARY_RADIUS in meters is:

PLANETARY_RADIUS = (DN * SCALING_FACTOR) + OFFSET,

where OFFSET is the radius of a reference sphere.

The planetopotential TOPOGRAPHY is:

PLANETARY_RADIUS – GEOID_RADIUS,

where GEOID_RADIUS is derived from a gravitational equipotential model.

By convention, the average GEOID_RADIUS at the equator is OFFSET.