GEOPHYSICAL RESEARCH LETTERS
Supporting Information for ”Data Drought in the
Humid Tropics: How to Overcome the Cloud Barrier
in Greenhouse Gas Remote Sensing”
C. Frankenberg
1
,
2
,
†
, Y. M. Bar-On
1
,
†
, Y. Yin
3
, P.O. Wennberg
1
,
4
, D.J.
Jacob
5
, A.M. Michalak
6
,
7
1
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
2
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
3
Department of Environmental Studies, New York University, New York, New York, USA
4
Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, USA
5
School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts, USA
6
Carnegie Institution for Science, Stanford, California, USA
7
Department of Earth System Science, Stanford University, Stanford, California, USA
†
Authors contributed equally to the study
Contents of this file
1. Text S1 to S4
2. Figures S1 to S8
Introduction
March 26, 2024, 8:26pm
X - 2
:
Our overall analysis was performed in the major tropical areas but many of the figures
in the main text only showed the Amazon. Here we provide a broader scope with a focus
on Africa and Southeast Asia as well. We also investigate potential optima in terms of
footprint sizes. We will show a visual guide of our analysis, a brief investigation into the
time-of-day dependency using OCO-3, as well as an evaluation of optimal footprint sizes.
Text S1: Visual representation.
Figure S1 provides a visual overview of our data analysis. Sentinel-2 images are acquired
every 5 days, resulting in 6 snapshots per month. These are displayed as matrix in the left
part of the figure, showing a 10x10km
2
area for clarity. For our analysis, we use the entire
image size within 1x1 degrees. The left column shows Sentinel 2 reflectances as false-color
image, with the reflectance at 835, 1610, and 2200 nm, respectively in red, green and blue.
These bands are close to the OCO-2 bands, thus the red-ness of the scene indicated much
higher O
2
A-band albedo compared to the CO
2
bands.
More than half of the scenes show typical shallow-cumulus cloud fields, which would
greatly benefit from smaller ground-pixels for GHG measurements. Only five are mostly
cloud-free, even for larger ground pixels than OCO-2 provides. A 2x2km area is indicated
in blue in the first column. The visualization supports the skewed distribution observed in
our statistical analysis. This results in long data-free periods during the wet season. The
right column shows our corresponding binary cloud filter, i.e. black areas are cloud-free
while white ones are either clouds or cloud shadows. Only one out of 72 images covering
a 10x10km
2
area is entirely cloud free.
Text S2: Impact of time-of-day on clouds and data yields.
March 26, 2024, 8:26pm