Validation is the generic term for any of a number of measurement activities designed to ensure that CloudSat measurements are well-characterized in terms of accuracy and uncertainty. Validation activities may be classified into several general types. Ground truth or truth data collection involves the direct measurement of geophysical parameters (such as cloud liquid water content) from ground-based or airborne probes for comparison to remote-sensing retrievals of the same quantities. Physical validation seeks to evaluate assumptions and parameter values (for example, the form of the drop size distribution or the effect of cloud structure) that are part of a remote-sensing retrieval but that are not directly measurable by the sensor. Correlative evaluation uses measurements from different remote sensors (often employing distinct retrieval methods using differing physical principles) to provide a check on the consistency of retrieved parameters. For example, the liquid water path retrieved from a visible radiance measurement might be compared to the liquid water path retrieved by a cloud radar.
The CloudSat validation plan relies on dovetailing into both systematic measurement programs (such as the U. S. Department of Energy's Atmospheric Radiation Measurements Program and measurements planned for selected sites within Europe and Japan) and planned field experiments (including NASA validation efforts as part of Aura and Aqua).
Key Field Programs
TWP-ICE - The Tropical Warm Pool-International Cloud Experiment was conducted over a four-week period in January-February 2006
in northern Australia. This was the first field program in the tropics that
attempts to describe the evolution of tropical convection through its life cycle,
including the large scale heat, moisture, and momentum budgets; detailed cloud
observations; and measurements of the impact of the cloud on the environment
with a special focus on radiative impacts and cirrus microphysics.
An extensive set of in-situ validation data for ARM ground-based and
NASA space-borne remote sensing systems was collected. The experiment is a
collaboration between the US DOE ARM Program, the (Australian) Bureau of
Meteorology, NASA, and several US and Australian universities. There was also
European involvement through a contemporaneous experiment, ACTIVE.
AMMA - The African Monsoon Multidisciplinary Analysis (AMMA) is an international project to improve our knowledge and understanding of the West African monsoon (WAM) and its variability, with an emphasis on daily-to-interannual timescales. AMMA is motivated by an interest in fundamental scientific issues and by the societal need for improved prediction of the WAM and its impacts on West African nations. AMMA promotes international coordination of ongoing activities, basic research and a multi-year field campaign over West Africa and the tropical Atlantic. At this time scientists from more than 20 countries, representing more than 40 national and pan-national agencies are involved in AMMA, and funding is largely secured in Europe up to 2010. Other international efforts are underway to help mobilize the extra funding needed to achieve all the AMMA aims.
C3VP - The Canadian CloudSat/CALIPSO Validation Project will undertake a thorough and careful evaluation of the
quality of the CloudSat products as they apply to Canadian climate. The
Meteorological Service of Canada (MSC) is the lead agency developing the
validation implementation plan, with support from the Canadian Space Agency.
The program will focus on stratiform cold-season cloud systems. These are
frequently mixed-phase in nature and occur throughout Canada much of the year.
The widespread and slowly changing nature of these systems are particularly well
suited to validation studies. Ground validation will be carried out over both
winters that CloudSat is in orbit. The aircraft campaign will focus on the first
Systematic Measurement Sites
CESAR - The Cabauw Experimental Sensing Area is sponsored by KNMI and other Dutch institutes (Delft, RIVM, etc.). CESAR instrumentation includes but is not limited to the following: wind profiler, IR radiometer, 3-GHz radar, 35-GHz radar, Raman lidar, scanning elastic scatter lidar, fixed elastic scatter lidar, GPS receiver, microwave radiometer, and tethered balloon.
ARM - The Atmospheric Radiation Measurements Program, funded by the U. S. Department of Energy, focuses on obtaining continuous
field measurements and providing data products that promote the
advancement of climate models. ARM has funded the development of
several highly instrumented ground stations for studying cloud formation
processes and their influence on radiative transfer, and for measuring other
parameters that determine the radiative properties of the atmosphere. Key
instruments include one of the few operational Raman lidars in the world;
millimeter-wavelength cloud radar; radar wind profilers; and total sky
imagers. More recent additions to the suite of ARM instrumentation are
the microwave radiometer and the advanced rotating shadowband
CloudNET is a research project supported by the European Commission
under the Fifth Framework Programme. This project, which started on 1 April 2001,
aims to use data obtained quasi-continuously for the
development and implementation of cloud remote sensing synergy
algorithms. The use of active instruments (lidar and radar) results in
detailed vertical profiles of important cloud parameters. CloudNET
consists of a network of three already-existing cloud remote sensing
stations in the Netherlands, the United Kingdom, and France.