Chandrayaan-1 MRFFR Map-Projected Calibrated Data Record (MAPCDR)

MAPCDR – Map-Projected Calibrated Data Record

Instrument: Forerunner

PDS3 Data Set ID: CH1-ORB-L-MRFFR-5-CDR-MAP-V1.0

PDS4 Bundle: urn:nasa:pds:chand1-orb_mini_rfDOI: 10.17189/1519033

Chandrayaan-1 Mini-RF archives PDS3 to PDS4 Migration Status: Complete

For more information about Forerunner PDR products, see the MAPCDR Data Set Description.

For more information about all Forerunner products, see the Data Product SIS.

The Forerunner (MRFFR) Map-Projected Calibrated Data Record (MAPCDR) data products are a time-ordered collection of calibrated Synthetic Aperture Radar (SAR) images collected by the instrument. They are provided in an oblique cylindrical map projection. The “equator” of the map projection will correspond to the line of longitude that the subspacecraft point crossed at the equator before the data collection. They also contain stokes parameters files, polarization ratio files, a radar albedo file, and a browse image.

All CDR images products are accompanied by four stokes parameters files. Forerunner transmits a right circular polarized signal, and receives H & V polarized signals, and the phase between the polarizations. The CDR file consists of four pieces of information per pixel. The received power in the horizontal polarization (E_RH), the received power in the vertical polarization (E_RV), and the real and imaginary portions of the cross product between the two polarization signals (ReE_RHE_RV* & ImE_RHE_RV*).

The four stokes parameters (S₁, S₂, S₃, and S₄) are related to the data in the CDR files by the following equations:

S₁ = <|E_RH|² + |E_RV|²>

S₂ = <|E_RH|² - |E_RV|²>

S₃ = 2Re<E_RHE_RV*>

S₄ = -2Im<E_RHE_RV*>

Forerunner transmits two orthogonal, linearly polarized waves with a phase shift of (nominally) one quarter of the wavelength, and the resulting superposition of these two forms a (nominally) circularly polarized beam.

The same-sense circular polarization product (SC) describes the polarization state of the received field that has an identical polarization to the transmitted beam. This product is calculated as one half of the difference between the Stokes S₁ and S₂ parameters (SC = 0.5S1 – 0.5S2).

The opposite sense circular polarization product (OC) describes the polarization state of the received field that has the opposite circular polarization to the transmitted beam. This product is calculated as one half of the sum of the Stokes S₁ and S₄ parameters (OC = 0.5S1 + 0.5S4).

The circular polarization ratio dimensionless parameter (CP) is the ratio of the same-sense circular polarization to the opposite-sense circular polarization (CP = SC/OC). The average CP value of the entire lunar surface is on the order of 0.3. CP values for certain types of surface deposits may be either anomalously low (near zero for very smooth terrain) or anomalously high (>1.0 for block large-scale rough features). High CP also is due to volumetric backscattering from thick deposits of frozen volatiles, such as water ice.

Degree of polarization (m): The fraction of radar backscatter that is polarized is given by the ratio m = (S₂² + S₃² + S₄²)^1/2/S₁. The average value of m at the moon is about 0.6.

MRFFR MAPCDR products have the following file names:

FSB_nnnnn_2tt_prU_aadooo_Vz.xxx (with one detached PDS label for both files)

where:

F = instrument = Forerunner

S = frequency band = S-band

B = radar mode = Baseline SAR

nnnnn = orbit number in which data acquisition began, numeric range 00001…99999

2 = processing level = MAPCDR

tt = file type

CD = Calibrated Data Records

S1 = Stokes Parameter 1 File

S2 = Stokes Parameter 2 File

S3 = Stokes Parameter 3 File

S4 = Stokes Parameter 4 File

SC = Same-Sense Polarization Image File

OC = Opposite-Sense Polarization Image File

CP = Circular Polarization Ratio Image File

p = projection

O = Oblique cylindrical

E = Equirectangular

r = pixel resolution bin scale in pixels per degree (ppd) and meters/pixel (mpd)

H = 128 ppd, 237 mpd

I = 256 ppd, 118 mpd

U = bit type and scaling = Unnormalized floating point

aa = lunar center latitude to nearest whole degree, numeric range 00…90, XX = N/A or Unknown

d = hemisphere of latitude

N = North latitude

S = South latitude

X = N/A

ooo = lunar center longitude to nearest whole degree, numeric range 000…359

z = product version number, numeric range 1…9

xxx = file extension

IMG = Processed image file

TXT = Unstructured text data (e.g., parameter files)

In ODE, MAPCDR products have the following product IDs:

FSB_NNNNN_1TT_PRU_AADOOO_VZ