Determination of cloud position in CERES products

[xwgw]

How to obtain cloud information in CERES 'product SYN1deg, because there is only cloud top height information, no cloud base height information, how to determine the position of the cloud? What is the effective height of the cloud and how is it defined?

[ASDC - cheyenne.e.land]

Hello,

Thank you for your interest in CERES data.

The cloud effective temperature of the cloud is the temperature returned from the Planck function using the observed imager radiance. The cloud effective height is the corresponding height you would find that temperature in the temperature profile. The cloud height is an adjustment to the effective cloud height based upon the cloud optical depth.

The cloud base pressure and temperature are provided which are used in the Fu-Liou radiative transfer calculations. You can get the cloud base height by using the hypsometric equation or by calculating a saturated adiabatic lapse rate at that point.

Regard,
ASDC

[xwgw]

Thank you very much for your answer. I am still a little confused, because I do not know how to calculate the saturated adiabatic lapse rate. Therefore, I would like to ask whether the geometric thickness of the cloud can be retrieved by using other micro-parameter information of the cloud (such as the effective radius of cloud particles, the visible thickness of cloud, etc.). Then, according to the difference between the height of the cloud top and the geometric thickness of the cloud, the height of the cloud base can be obtained (because the long-wave radiation is related to the height of the cloud base). Is there any specific literature or anything like that that has a specific method? In addition, I want to know that the long-wave radiation, that is, the difference in radiation flux between the total channel and the short-wave channel?

[xwgw]

What is the relationship between cloud effective temperature, cloud effective altitude, cloud effective pressure and cloud radiation? Is the effective temperature and height of the cloud information used to represent the temperature in the cloud and the geometric thickness of the cloud?

[ASDC - cheyenne.e.land]

Hello,

We contacted a member of the CERES Science team and they have stated:

CERES and the imager measurements are satellite based and they are measuring the radiation emitted near the top of the cloud. Therefore, the window channel imager radiance after having atmospheric corrections applied is used to obtain the cloud effective temperature using the inverse Plank function. The temperature, height, and pressure profiles from the Global Modeling and Assimilation Office are used to obtain the pressure and height that the retrieved effective temperature is located through linear interpolation.

I did locate the empirical relationship that is used to calculate cloud thickness in km used in our processing:

For water clouds with optical depth > 1: Cloud Thickness = 0.39 * ln(COD) - 0.1

optical depth <= 1: Cloud Thickness = 0.05 * SQRT(COD)

For ice clouds colder than 245 K: Cloud Thickness = 7.2 - 0.024 * Cloud Effective Temp + 0.95 * ln(COD)

The minimum cloud thickness is 0.02 km in either case.

The cloud thickness is subtracted from the cloud top height to get the cloud base.

The SYN1deg does not have broadband radiances due to the angular dependence involved. Also, most hours do not have CERES flux measurements, but values obtained from either narrowband to broadband fluxes based on geostationary imager radiance or interpolation. The radiance information is on the SSF or SSF1deg-Hour products.

The articles covering the cloud retrievals are

Minnis, P., S. Sun-Mack, Y. Chen, F. Chang, C. R. Yost, W. L. Smith, P. W. Heck, R. F. Arduini, S. T. Bedka, Y. Yi, G. Hong, Z. Jin, D. Painemal, R. Palikonda, B. R. Scarino, D. A. Spangenberg, R. A. Smith, Q. Z. Trepte, P. Yang, Y. Xie, 2020: CERES MODIS Cloud Product Retrievals for Edition 4–Part I: Algorithm Changes. IEEE Transactions on Geoscience and Remote Sensing, 1-37. doi: 10.1109/TGRS.2020.3008866

Minnis, P., S. Sun-Mack, D. Young, P. Heck, D. Garber, Y. Chen, D. Spangenberg, R. Arduini, Q. Trepte, W. Smith, J. Ayers, S. Gibson, W. Miller, G. Hong, V. Chakrapani, Y. Takano, K. Liou, Y. Xie, P. Yang, 2011: CERES Edition-2 Cloud Property Retrievals Using TRMM VIRS and Terra and Aqua MODIS Data #x2014;Part I: Algorithms. IEEE Transactions on Geoscience and Remote Sensing, 49(11), 4374-4400. doi: 10.1109/TGRS.2011.2144601.

[xwgw]

Hello, I still have some questions to ask you, that is, in the cloud parameter information, how to choose and define the optical thickness of the cloud and the effective radius of the cloud droplet particles, because SSF in the single footprint satellite product provides the logarithmic visible optical thickness of 3 different wavelength channels.
Among them, cloud optical thickness is 0.65 micron visible optical thickness, log visible optical thickness, log visible optical depth 1.2 micron, log visible optical thickness 2.1 micron. I would like to ask how the cloud optical thickness of these three different channels is selected when studying the radiation flux information of cloud length and short wavelength top atmosphere and surface. Do we only consider the visible optical thickness at 0.65 microns for short wave? Do you need to consider the short-wave infrared of 0.65 microns and 2.1 microns in visible light for long wave, or do you need to consider the visible optical thickness of 3 different wavelength bands? In addition, I would like to ask because the CERES instrument carried on the Terra satellite platform does not have a direct long-wave channel, I would like to know how the radiation flux of the long-wave channel is defined and calculated, and what is the difference between night and day?
For cloud particle radius, there are two states: ice particle and water particle, and they have three different channels, namely 1.2 micron, 2.1 micron, 3.7 micron liquid particle radius and ice water particle radius. I have learned that cloud droplet particle radius has an impact on long wave and short wave radiation flux, so when I simulate long wave and short wave radiation flux information, How to select the particle radius information of cloud droplets? Since the liquid water path and ice water path provided are 3.7 micron channels, do I directly select the radius information of liquid water particles and ice water particles in 3.7 micron channels?
My idea is that when selecting cloud particle radius information, 1 represents water phase state, 2 represents ice phase state, and 1-2 is mixed phase state according to the distinction of cloud phase states, then I will obtain the particle radius information value of the corresponding channel according to the division of different phase states, and then simulate the long and short wave radiation flux information. Is this idea correct?
Finally, I would like to know that when calculating cloud thickness information you mentioned before, according to the empirical formula:
For water clouds with optical depth > 1: Cloud thickness = 0.39 * ln (COD) -0.1
Optical depth <= 1: Cloud thickness = 0.05 * SQRT (COD)
For ice clouds below 245 K: Cloud thickness = 7.2-0.024 * Cloud effective temperature + 0.95 * ln (COD)
In either case, the minimum cloud thickness is 0.02 km.
Subtract the thickness of the cloud from the height of the cloud top to get the cloud base.
For single-footprint satellite product SSF, which channel is the optical thickness selected, is it the visible optical thickness?
Sorry for the many questions I have, but it is very important to me. I really hope to get your help, thank you, and hope to receive your reply soon.

[ASDC - cheyenne.e.land]

Hello,

On the CERES Website, the documentation section is a great resource for the questions that you have. It includes a General CERES References, Data Product References, Data Quality Summaries, Data Products Catalog, Data Collection Guides, CERES Algorithm Theoretical Basis Documents, and Historical Documents.

Regards,
ASDC